[PATCH V4 0/3] perf tools and x86 PTI entry trampolines

[PATCH V4 0/3] perf tools and x86 PTI entry trampolines

[Adrian Hunter]

Hi

Here is V4 of patches to support x86 PTI entry trampolines in perf tools.

Patches also here:
	http://git.infradead.org/users/ahunter/linux-perf.git/shortlog/refs/heads/perf-tools-kpti-v4
	git://git.infradead.org/users/ahunter/linux-perf.git perf-tools-kpti-v4

V3 patches also here:
	http://git.infradead.org/users/ahunter/linux-perf.git/shortlog/refs/heads/perf-tools-kpti-v3
	git://git.infradead.org/users/ahunter/linux-perf.git perf-tools-kpti-v3

V2 patches also here:
	http://git.infradead.org/users/ahunter/linux-perf.git/shortlog/refs/heads/perf-tools-kpti-v2
	git://git.infradead.org/users/ahunter/linux-perf.git perf-tools-kpti-v2

V1 patches also here:
	http://git.infradead.org/users/ahunter/linux-perf.git/shortlog/refs/heads/perf-tools-kpti-v1
	git://git.infradead.org/users/ahunter/linux-perf.git perf-tools-kpti-v1


Changes Since V3:
	kallsyms: Simplify update_iter_mod()
		Added comment
		Added Andi's Ack

	kallsyms, x86: Export addresses of PTI entry trampolines
		Expanded commit message
		Used for_each_possible_cpu()
		Added Andi's Ack even though logic changed slightly

	x86: Add entry trampolines to kcore
		Re-based
		Added Andi's Ack

	perf tools: Add machine__nr_cpus_avail()
	perf tools: Workaround missing maps for x86 PTI entry trampolines
	perf tools: Fix map_groups__split_kallsyms() for entry trampoline symbols
	perf tools: Allow for extra kernel maps
	perf tools: Create maps for x86 PTI entry trampolines
	perf tools: Synthesize and process mmap events for x86 PTI entry trampolines
	perf buildid-cache: kcore_copy: Keep phdr data in a list
	perf buildid-cache: kcore_copy: Keep a count of phdrs
	perf buildid-cache: kcore_copy: Calculate offset from phnum
	perf buildid-cache: kcore_copy: Layout sections
	perf buildid-cache: kcore_copy: Iterate phdrs
	perf buildid-cache: kcore_copy: Get rid of kernel_map
	perf buildid-cache: kcore_copy: Copy x86 PTI entry trampoline sections
	perf buildid-cache: kcore_copy: Amend the offset of sections that remap kernel text
		Dropped because they have been applied

Changes Since V2:

	x86: Add entry trampolines to kcore
	x86: kcore: Give entry trampolines all the same offset in kcore
		Combined into a single patch
		Added comment
		Expand commit message

	perf tools: Add machine__is() to identify machine arch
		Dropped because it has been applied

	perf tools: Fix kernel_start for PTI on x86
		Dropped because it has been applied

Changes Since V1:

	perf tools: Use the _stest symbol to identify the kernel map when loading kcore
		Dropped because it has been applied

	perf tools: Add machine__is() to identify machine arch
		New patch

	perf tools: Fix kernel_start for PTI on x86
		Moved definition of machine__is() to a separate patch

	perf tools: Add machine__nr_cpus_avail()
		New patch

	perf tools: Workaround missing maps for x86 PTI entry trampolines
		Use machine__nr_cpus_avail()

	perf tools: Create maps for x86 PTI entry trampolines
		Re-based

Changes Since RFC:

	Change description 'x86_64 KPTI' to 'x86 PTI'

	Rename 'special' kernel map to 'extra' kernel map etc

	kallsyms: Simplify update_iter_mod()
		Expand commit message

	perf tools: Fix kernel_start for PTI on x86
		Amend machine__is() to check if machine is NULL

	perf tools: Workaround missing maps for x86 PTI entry trampolines
		Simplify find_entry_trampoline()
		Add comment before struct extra_kernel_map /* Kernel-space
		maps for symbols that are outside the main kernel map and
		module maps */

	perf tools: Create maps for x86 PTI entry trampolines
		Move code presently only used by x86_64 into arch

	perf tools: Synthesize and process mmap events for x86 PTI entry
	trampolines
		Fix spelling 'kernal' -> 'kernel'
		Rename 'special' kernel map to 'extra' kernel map etc
		Move code presently only used by x86_64 into arch

	perf buildid-cache: kcore_copy: Keep phdr data in a list
		Expand commit message
		Rename 'list' -> 'node'

	perf buildid-cache: kcore_copy: Get rid of kernel_map
		Expand commit message
		Add phdr_data__new()
		Rename 'kcore_copy__new_phdr' -> 'kcore_copy_info__addnew'


Original Cover email:

Perf tools do not know about x86 PTI entry trampolines - see example
below.  These patches add a workaround, namely "perf tools: Workaround
missing maps for x86 PTI entry trampolines", which has the limitation
that it hard codes the addresses.  Note that the workaround will work for
old kernels and old perf.data files, but not for future kernels if the
trampoline addresses are ever changed.

At present, perf tools uses /proc/kallsyms to construct a memory map for
the kernel.  Recording such a map in the perf.data file is necessary to
deal with kernel relocation and KASLR.

While it is reasonable on its own terms, to add symbols for the trampolines
to /proc/kallsyms, the motivation here is to have perf tools use them to
create memory maps in the same fashion as is done for the kernel text.

So the first 2 patches add symbols to /proc/kallsyms for the trampolines:

      kallsyms: Simplify update_iter_mod()
      kallsyms, x86: Export addresses of syscall trampolines

perf tools have the ability to use /proc/kcore (in conjunction with
/proc/kallsyms) as the kernel image. So the next 2 patches add program
headers for the trampolines to the kcore ELF:

      x86: Add entry trampolines to kcore
      x86: kcore: Give entry trampolines all the same offset in kcore

It is worth noting that, with the kcore changes alone, perf tools require
no changes to recognise the trampolines when using /proc/kcore.

Similarly, if perf tools are used with a matching kallsyms only (by denying
access to /proc/kcore or a vmlinux image), then the kallsyms patches are
sufficient to recognise the trampolines with no changes needed to the
tools.

However, in the general case, when using vmlinux or dealing with
relocations, perf tools needs memory maps for the trampolines.  Because the
kernel text map is constructed as a special case, using the same approach
for the trampolines means treating them as a special case also, which
requires a number of changes to perf tools, and the remaining patches deal
with that.


Example: make a program that does lots of small syscalls e.g.

	$ cat uname_x_n.c

	#include <sys/utsname.h>
	#include <stdlib.h>

	int main(int argc, char *argv[])
	{
		long n = argc > 1 ? strtol(argv[1], NULL, 0) : 0;
		struct utsname u;

		while (n--)
			uname(&u);

		return 0;
	}

and then:

	sudo perf record uname_x_n 100000
	sudo perf report --stdio

Before the changes, there are unknown symbols:

 # Overhead  Command    Shared Object     Symbol
 # ........  .........  ................  ..................................
 #
    41.91%  uname_x_n  [kernel.vmlinux]  [k] syscall_return_via_sysret
    19.22%  uname_x_n  [kernel.vmlinux]  [k] copy_user_enhanced_fast_string
    18.70%  uname_x_n  [unknown]         [k] 0xfffffe00000e201b
     4.09%  uname_x_n  libc-2.19.so      [.] __GI___uname
     3.08%  uname_x_n  [kernel.vmlinux]  [k] do_syscall_64
     3.02%  uname_x_n  [unknown]         [k] 0xfffffe00000e2025
     2.32%  uname_x_n  [kernel.vmlinux]  [k] down_read
     2.27%  uname_x_n  ld-2.19.so        [.] _dl_start
     1.97%  uname_x_n  [unknown]         [k] 0xfffffe00000e201e
     1.25%  uname_x_n  [kernel.vmlinux]  [k] up_read
     1.02%  uname_x_n  [unknown]         [k] 0xfffffe00000e200c
     0.99%  uname_x_n  [kernel.vmlinux]  [k] entry_SYSCALL_64
     0.16%  uname_x_n  [kernel.vmlinux]  [k] flush_signal_handlers
     0.01%  perf       [kernel.vmlinux]  [k] native_sched_clock
     0.00%  perf       [kernel.vmlinux]  [k] native_write_msr

After the changes there are not:

 # Overhead  Command    Shared Object     Symbol
 # ........  .........  ................  ..................................
 #
    41.91%  uname_x_n  [kernel.vmlinux]  [k] syscall_return_via_sysret
    24.70%  uname_x_n  [kernel.vmlinux]  [k] entry_SYSCALL_64_trampoline
    19.22%  uname_x_n  [kernel.vmlinux]  [k] copy_user_enhanced_fast_string
     4.09%  uname_x_n  libc-2.19.so      [.] __GI___uname
     3.08%  uname_x_n  [kernel.vmlinux]  [k] do_syscall_64
     2.32%  uname_x_n  [kernel.vmlinux]  [k] down_read
     2.27%  uname_x_n  ld-2.19.so        [.] _dl_start
     1.25%  uname_x_n  [kernel.vmlinux]  [k] up_read
     0.99%  uname_x_n  [kernel.vmlinux]  [k] entry_SYSCALL_64
     0.16%  uname_x_n  [kernel.vmlinux]  [k] flush_signal_handlers
     0.01%  perf       [kernel.vmlinux]  [k] native_sched_clock
     0.00%  perf       [kernel.vmlinux]  [k] native_write_msr


Adrian Hunter (2):
      kallsyms: Simplify update_iter_mod()
      x86: Add entry trampolines to kcore

Alexander Shishkin (1):
      kallsyms, x86: Export addresses of PTI entry trampolines

 arch/x86/mm/cpu_entry_area.c | 33 ++++++++++++++++++++++++++++
 fs/proc/kcore.c              |  7 ++++--
 include/linux/kcore.h        | 13 +++++++++++
 kernel/kallsyms.c            | 51 ++++++++++++++++++++++++++++++++------------
 4 files changed, 88 insertions(+), 16 deletions(-)


Regards
Adrian

[PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Adrian Hunter]

The logic in update_iter_mod() is overcomplicated and gets worse every time
another get_ksymbol_* function is added.

In preparation for adding another get_ksymbol_* function, simplify logic in
update_iter_mod().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
---
 kernel/kallsyms.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index a23e21ada81b..aa31aa07f2ef 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -506,27 +506,24 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 	}
 }
 
+/*
+ * The end position (last + 1) of each additional kallsyms section is recorded
+ * in iter->pos_..._end as each section is added, and so can be used to
+ * determine which get_ksymbol_...() function to call next.
+ */
 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 {
 	iter->pos = pos;
 
-	if (iter->pos_ftrace_mod_end > 0 &&
-	    iter->pos_ftrace_mod_end < iter->pos)
-		return get_ksymbol_bpf(iter);
-
-	if (iter->pos_mod_end > 0 &&
-	    iter->pos_mod_end < iter->pos) {
-		if (!get_ksymbol_ftrace_mod(iter))
-			return get_ksymbol_bpf(iter);
+	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
+	    get_ksymbol_mod(iter))
 		return 1;
-	}
 
-	if (!get_ksymbol_mod(iter)) {
-		if (!get_ksymbol_ftrace_mod(iter))
-			return get_ksymbol_bpf(iter);
-	}
+	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
+	    get_ksymbol_ftrace_mod(iter))
+		return 1;
 
-	return 1;
+	return get_ksymbol_bpf(iter);
 }
 
 /* Returns false if pos at or past end of file. */
-- 
1.9.1

[PATCH V4 2/3] kallsyms, x86: Export addresses of PTI entry trampolines

[Adrian Hunter]

From: Alexander Shishkin <alexander.shishkin@linux.intel.com>

Currently, the addresses of PTI entry trampolines are not exported to user
space. Kernel profiling tools need these addresses to identify the kernel
code, so add a symbol and address for each CPU's PTI entry trampoline.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/mm/cpu_entry_area.c | 23 +++++++++++++++++++++++
 kernel/kallsyms.c            | 28 +++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index b45f5aaefd74..fab49fd5190f 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -2,6 +2,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
+#include <linux/kallsyms.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/pgtable.h>
@@ -150,6 +151,28 @@ static void __init setup_cpu_entry_area(int cpu)
 	percpu_setup_debug_store(cpu);
 }
 
+#ifdef CONFIG_X86_64
+int arch_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+		     char *name)
+{
+	unsigned int cpu, ncpu = 0;
+
+	if (symnum >= num_possible_cpus())
+		return -EINVAL;
+
+	for_each_possible_cpu(cpu) {
+		if (ncpu++ >= symnum)
+			break;
+	}
+
+	*value = (unsigned long)&get_cpu_entry_area(cpu)->entry_trampoline;
+	*type = 't';
+	strlcpy(name, "__entry_SYSCALL_64_trampoline", KSYM_NAME_LEN);
+
+	return 0;
+}
+#endif
+
 static __init void setup_cpu_entry_area_ptes(void)
 {
 #ifdef CONFIG_X86_32
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index aa31aa07f2ef..02a0b01380d8 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -432,6 +432,7 @@ int sprint_backtrace(char *buffer, unsigned long address)
 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 struct kallsym_iter {
 	loff_t pos;
+	loff_t pos_arch_end;
 	loff_t pos_mod_end;
 	loff_t pos_ftrace_mod_end;
 	unsigned long value;
@@ -443,9 +444,29 @@ struct kallsym_iter {
 	int show_value;
 };
 
+int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
+			    char *type, char *name)
+{
+	return -EINVAL;
+}
+
+static int get_ksymbol_arch(struct kallsym_iter *iter)
+{
+	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
+				   &iter->value, &iter->type,
+				   iter->name);
+
+	if (ret < 0) {
+		iter->pos_arch_end = iter->pos;
+		return 0;
+	}
+
+	return 1;
+}
+
 static int get_ksymbol_mod(struct kallsym_iter *iter)
 {
-	int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
+	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 				     &iter->value, &iter->type,
 				     iter->name, iter->module_name,
 				     &iter->exported);
@@ -501,6 +522,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 	iter->nameoff = get_symbol_offset(new_pos);
 	iter->pos = new_pos;
 	if (new_pos == 0) {
+		iter->pos_arch_end = 0;
 		iter->pos_mod_end = 0;
 		iter->pos_ftrace_mod_end = 0;
 	}
@@ -515,6 +537,10 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 {
 	iter->pos = pos;
 
+	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
+	    get_ksymbol_arch(iter))
+		return 1;
+
 	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 	    get_ksymbol_mod(iter))
 		return 1;
-- 
1.9.1

[PATCH V4 3/3] x86: Add entry trampolines to kcore

[Adrian Hunter]

Without program headers for PTI entry trampoline pages, the trampoline
virtual addresses do not map to anything.

Example before:

 sudo gdb --quiet vmlinux /proc/kcore
 Reading symbols from vmlinux...done.
 [New process 1]
 Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.16.0 root=UUID=a6096b83-b763-4101-807e-f33daff63233'.
 #0  0x0000000000000000 in irq_stack_union ()
 (gdb) x /21ib 0xfffffe0000006000
    0xfffffe0000006000:  Cannot access memory at address 0xfffffe0000006000
 (gdb) quit

After:

 sudo gdb --quiet vmlinux /proc/kcore
 [sudo] password for ahunter:
 Reading symbols from vmlinux...done.
 [New process 1]
 Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.16.0-fix-4-00005-gd6e65a8b4072 root=UUID=a6096b83-b7'.
 #0  0x0000000000000000 in irq_stack_union ()
 (gdb) x /21ib 0xfffffe0000006000
    0xfffffe0000006000:  swapgs
    0xfffffe0000006003:  mov    %rsp,-0x3e12(%rip)        # 0xfffffe00000021f8
    0xfffffe000000600a:  xchg   %ax,%ax
    0xfffffe000000600c:  mov    %cr3,%rsp
    0xfffffe000000600f:  bts    $0x3f,%rsp
    0xfffffe0000006014:  and    $0xffffffffffffe7ff,%rsp
    0xfffffe000000601b:  mov    %rsp,%cr3
    0xfffffe000000601e:  mov    -0x3019(%rip),%rsp        # 0xfffffe000000300c
    0xfffffe0000006025:  pushq  $0x2b
    0xfffffe0000006027:  pushq  -0x3e35(%rip)        # 0xfffffe00000021f8
    0xfffffe000000602d:  push   %r11
    0xfffffe000000602f:  pushq  $0x33
    0xfffffe0000006031:  push   %rcx
    0xfffffe0000006032:  push   %rdi
    0xfffffe0000006033:  mov    $0xffffffff91a00010,%rdi
    0xfffffe000000603a:  callq  0xfffffe0000006046
    0xfffffe000000603f:  pause
    0xfffffe0000006041:  lfence
    0xfffffe0000006044:  jmp    0xfffffe000000603f
    0xfffffe0000006046:  mov    %rdi,(%rsp)
    0xfffffe000000604a:  retq
 (gdb) quit

In addition, entry trampolines all map to the same page.  Represent that by
giving the corresponding program headers in kcore the same offset.

This has the benefit that, when perf tools uses /proc/kcore as a source for
kernel object code, samples from different CPU trampolines are aggregated
together.  Note, such aggregation is normal for profiling i.e. people want
to profile the object code, not every different virtual address the object
code might be mapped to (across different processes for example).

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
 fs/proc/kcore.c              |  7 +++++--
 include/linux/kcore.h        | 13 +++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index fab49fd5190f..076ebdce9bd4 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -3,6 +3,7 @@
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
 #include <linux/kallsyms.h>
+#include <linux/kcore.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/pgtable.h>
@@ -14,6 +15,7 @@
 #ifdef CONFIG_X86_64
 static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
 	[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
+static DEFINE_PER_CPU(struct kcore_list, kcore_entry_trampoline);
 #endif
 
 struct cpu_entry_area *get_cpu_entry_area(int cpu)
@@ -147,6 +149,14 @@ static void __init setup_cpu_entry_area(int cpu)
 
 	cea_set_pte(&get_cpu_entry_area(cpu)->entry_trampoline,
 		     __pa_symbol(_entry_trampoline), PAGE_KERNEL_RX);
+	/*
+	 * The cpu_entry_area alias addresses are not in the kernel binary
+	 * so they do not show up in /proc/kcore normally.  This adds entries
+	 * for them manually.
+	 */
+	kclist_add_remap(&per_cpu(kcore_entry_trampoline, cpu),
+			 _entry_trampoline,
+			 &get_cpu_entry_area(cpu)->entry_trampoline, PAGE_SIZE);
 #endif
 	percpu_setup_debug_store(cpu);
 }
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index e64ecb9f2720..00282f134336 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -383,8 +383,11 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
 		phdr->p_type	= PT_LOAD;
 		phdr->p_flags	= PF_R|PF_W|PF_X;
 		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
-		phdr->p_vaddr	= (size_t)m->addr;
-		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
+		if (m->type == KCORE_REMAP)
+			phdr->p_vaddr	= (size_t)m->vaddr;
+		else
+			phdr->p_vaddr	= (size_t)m->addr;
+		if (m->type == KCORE_RAM || m->type == KCORE_TEXT || m->type == KCORE_REMAP)
 			phdr->p_paddr	= __pa(m->addr);
 		else
 			phdr->p_paddr	= (elf_addr_t)-1;
diff --git a/include/linux/kcore.h b/include/linux/kcore.h
index 80db19d3a505..3a11ce51e137 100644
--- a/include/linux/kcore.h
+++ b/include/linux/kcore.h
@@ -12,11 +12,13 @@ enum kcore_type {
 	KCORE_VMEMMAP,
 	KCORE_USER,
 	KCORE_OTHER,
+	KCORE_REMAP,
 };
 
 struct kcore_list {
 	struct list_head list;
 	unsigned long addr;
+	unsigned long vaddr;
 	size_t size;
 	int type;
 };
@@ -30,11 +32,22 @@ struct vmcore {
 
 #ifdef CONFIG_PROC_KCORE
 extern void kclist_add(struct kcore_list *, void *, size_t, int type);
+static inline
+void kclist_add_remap(struct kcore_list *m, void *addr, void *vaddr, size_t sz)
+{
+	m->vaddr = (unsigned long)vaddr;
+	kclist_add(m, addr, sz, KCORE_REMAP);
+}
 #else
 static inline
 void kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 {
 }
+
+static inline
+void kclist_add_remap(struct kcore_list *m, void *addr, void *vaddr, size_t sz)
+{
+}
 #endif
 
 #endif /* _LINUX_KCORE_H */
-- 
1.9.1

Re: [PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Peter Zijlstra]

On Wed, Jun 06, 2018 at 03:54:09PM +0300, Adrian Hunter wrote:
> The logic in update_iter_mod() is overcomplicated and gets worse every time
> another get_ksymbol_* function is added.
> 
> In preparation for adding another get_ksymbol_* function, simplify logic in
> update_iter_mod().
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> Acked-by: Andi Kleen <ak@linux.intel.com>

Both Daniel and Steven touched this function last year, let's also Cc
them.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> ---
>  kernel/kallsyms.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index a23e21ada81b..aa31aa07f2ef 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -506,27 +506,24 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
>  	}
>  }
>  
> +/*
> + * The end position (last + 1) of each additional kallsyms section is recorded
> + * in iter->pos_..._end as each section is added, and so can be used to
> + * determine which get_ksymbol_...() function to call next.
> + */
>  static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
>  {
>  	iter->pos = pos;
>  
> -	if (iter->pos_ftrace_mod_end > 0 &&
> -	    iter->pos_ftrace_mod_end < iter->pos)
> -		return get_ksymbol_bpf(iter);
> -
> -	if (iter->pos_mod_end > 0 &&
> -	    iter->pos_mod_end < iter->pos) {
> -		if (!get_ksymbol_ftrace_mod(iter))
> -			return get_ksymbol_bpf(iter);
> +	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
> +	    get_ksymbol_mod(iter))
>  		return 1;
> -	}
>  
> -	if (!get_ksymbol_mod(iter)) {
> -		if (!get_ksymbol_ftrace_mod(iter))
> -			return get_ksymbol_bpf(iter);
> -	}
> +	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
> +	    get_ksymbol_ftrace_mod(iter))
> +		return 1;
>  
> -	return 1;
> +	return get_ksymbol_bpf(iter);
>  }
>  
>  /* Returns false if pos at or past end of file. */
> -- 
> 1.9.1
> 

Re: [PATCH V4 2/3] kallsyms, x86: Export addresses of PTI entry trampolines

[Peter Zijlstra]

On Wed, Jun 06, 2018 at 03:54:10PM +0300, Adrian Hunter wrote:
> From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> 
> Currently, the addresses of PTI entry trampolines are not exported to user
> space. Kernel profiling tools need these addresses to identify the kernel
> code, so add a symbol and address for each CPU's PTI entry trampoline.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Acked-by: Andi Kleen <ak@linux.intel.com>

Thanks for the Changelog,

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

[Peter Zijlstra]

On Wed, Jun 06, 2018 at 03:54:11PM +0300, Adrian Hunter wrote:
> Without program headers for PTI entry trampoline pages, the trampoline
> virtual addresses do not map to anything.
> 

> 
> In addition, entry trampolines all map to the same page.  Represent that by
> giving the corresponding program headers in kcore the same offset.
> 
> This has the benefit that, when perf tools uses /proc/kcore as a source for
> kernel object code, samples from different CPU trampolines are aggregated
> together.  Note, such aggregation is normal for profiling i.e. people want
> to profile the object code, not every different virtual address the object
> code might be mapped to (across different processes for example).
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> Acked-by: Andi Kleen <ak@linux.intel.com>
> ---
>  arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
>  fs/proc/kcore.c              |  7 +++++--
>  include/linux/kcore.h        | 13 +++++++++++++
>  3 files changed, 28 insertions(+), 2 deletions(-)

This also adds the KCORE_REMAP functionality, but isn't mentioned at all
in the Changelog.

Still, looks OK I suppose,

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

[Arnaldo Carvalho de Melo]

Em Wed, Jun 06, 2018 at 03:16:31PM +0200, Peter Zijlstra escreveu:
> On Wed, Jun 06, 2018 at 03:54:11PM +0300, Adrian Hunter wrote:
> > Without program headers for PTI entry trampoline pages, the trampoline
> > virtual addresses do not map to anything.
> > 
> 
> > 
> > In addition, entry trampolines all map to the same page.  Represent that by
> > giving the corresponding program headers in kcore the same offset.
> > 
> > This has the benefit that, when perf tools uses /proc/kcore as a source for
> > kernel object code, samples from different CPU trampolines are aggregated
> > together.  Note, such aggregation is normal for profiling i.e. people want
> > to profile the object code, not every different virtual address the object
> > code might be mapped to (across different processes for example).
> > 
> > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> > Acked-by: Andi Kleen <ak@linux.intel.com>
> > ---
> >  arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
> >  fs/proc/kcore.c              |  7 +++++--
> >  include/linux/kcore.h        | 13 +++++++++++++
> >  3 files changed, 28 insertions(+), 2 deletions(-)
> 
> This also adds the KCORE_REMAP functionality, but isn't mentioned at all
> in the Changelog.
> 
> Still, looks OK I suppose,

I can add a note about that,
 
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Thanks, giving it some more hours and will apply and try to test it.

- Arnaldo

Re: [PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Steven Rostedt]

On Wed, 6 Jun 2018 15:13:02 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Jun 06, 2018 at 03:54:09PM +0300, Adrian Hunter wrote:
> > The logic in update_iter_mod() is overcomplicated and gets worse every time
> > another get_ksymbol_* function is added.
> > 
> > In preparation for adding another get_ksymbol_* function, simplify logic in
> > update_iter_mod().
> > 
> > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> > Acked-by: Andi Kleen <ak@linux.intel.com>  
> 
> Both Daniel and Steven touched this function last year, let's also Cc
> them.

Thanks for Ccing me. I tested the patch to make sure my changes still
work and they do:

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve


> 
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Arnaldo Carvalho de Melo]

Em Wed, Jun 06, 2018 at 02:37:27PM -0400, Steven Rostedt escreveu:
> On Wed, 6 Jun 2018 15:13:02 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Wed, Jun 06, 2018 at 03:54:09PM +0300, Adrian Hunter wrote:
> > > The logic in update_iter_mod() is overcomplicated and gets worse every time
> > > another get_ksymbol_* function is added.
> > > 
> > > In preparation for adding another get_ksymbol_* function, simplify logic in
> > > update_iter_mod().
> > > 
> > > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> > > Acked-by: Andi Kleen <ak@linux.intel.com>  
> > 
> > Both Daniel and Steven touched this function last year, let's also Cc
> > them.
> 
> Thanks for Ccing me. I tested the patch to make sure my changes still
> work and they do:
> 
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Since you said you tested the patch, may I replace the Acked-by with the
stronger Tested-by?

Thanks,

- Arnaldo

Re: [PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Steven Rostedt]

On Wed, 6 Jun 2018 15:59:14 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Em Wed, Jun 06, 2018 at 02:37:27PM -0400, Steven Rostedt escreveu:
> > On Wed, 6 Jun 2018 15:13:02 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> >   
> > > On Wed, Jun 06, 2018 at 03:54:09PM +0300, Adrian Hunter wrote:  
> > > > The logic in update_iter_mod() is overcomplicated and gets worse every time
> > > > another get_ksymbol_* function is added.
> > > > 
> > > > In preparation for adding another get_ksymbol_* function, simplify logic in
> > > > update_iter_mod().
> > > > 
> > > > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> > > > Acked-by: Andi Kleen <ak@linux.intel.com>    
> > > 
> > > Both Daniel and Steven touched this function last year, let's also Cc
> > > them.  
> > 
> > Thanks for Ccing me. I tested the patch to make sure my changes still
> > work and they do:
> > 
> > Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>  
> 
> Since you said you tested the patch, may I replace the Acked-by with the
> stronger Tested-by?

Well, I only tested it against the changes I made earlier. I didn't do
any other testing, which is why I'm reluctant to say "tested by".

Perhaps it can be:

Tested-by: (ftrace changes only) Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

Re: [PATCH V4 1/3] kallsyms: Simplify update_iter_mod()

[Arnaldo Carvalho de Melo]

Em Wed, Jun 06, 2018 at 03:13:00PM -0400, Steven Rostedt escreveu:
> On Wed, 6 Jun 2018 15:59:14 -0300
> Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> 
> > Em Wed, Jun 06, 2018 at 02:37:27PM -0400, Steven Rostedt escreveu:
> > > On Wed, 6 Jun 2018 15:13:02 +0200
> > > Peter Zijlstra <peterz@infradead.org> wrote:
> > >   
> > > > On Wed, Jun 06, 2018 at 03:54:09PM +0300, Adrian Hunter wrote:  
> > > > > The logic in update_iter_mod() is overcomplicated and gets worse every time
> > > > > another get_ksymbol_* function is added.
> > > > > 
> > > > > In preparation for adding another get_ksymbol_* function, simplify logic in
> > > > > update_iter_mod().
> > > > > 
> > > > > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> > > > > Acked-by: Andi Kleen <ak@linux.intel.com>    
> > > > 
> > > > Both Daniel and Steven touched this function last year, let's also Cc
> > > > them.  
> > > 
> > > Thanks for Ccing me. I tested the patch to make sure my changes still
> > > work and they do:
> > > 
> > > Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>  
> > 
> > Since you said you tested the patch, may I replace the Acked-by with the
> > stronger Tested-by?
> 
> Well, I only tested it against the changes I made earlier. I didn't do
> any other testing, which is why I'm reluctant to say "tested by".
> 
> Perhaps it can be:
> 
> Tested-by: (ftrace changes only) Steven Rostedt (VMware) <rostedt@goodmis.org>

I think that brings more useful information to the log, so should be
useful.

- Arnaldo

Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

[Adrian Hunter]

On 06/06/18 16:19, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 06, 2018 at 03:16:31PM +0200, Peter Zijlstra escreveu:
>> On Wed, Jun 06, 2018 at 03:54:11PM +0300, Adrian Hunter wrote:
>>> Without program headers for PTI entry trampoline pages, the trampoline
>>> virtual addresses do not map to anything.
>>>
>>
>>>
>>> In addition, entry trampolines all map to the same page.  Represent that by
>>> giving the corresponding program headers in kcore the same offset.
>>>
>>> This has the benefit that, when perf tools uses /proc/kcore as a source for
>>> kernel object code, samples from different CPU trampolines are aggregated
>>> together.  Note, such aggregation is normal for profiling i.e. people want
>>> to profile the object code, not every different virtual address the object
>>> code might be mapped to (across different processes for example).
>>>
>>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>>> Acked-by: Andi Kleen <ak@linux.intel.com>
>>> ---
>>>  arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
>>>  fs/proc/kcore.c              |  7 +++++--
>>>  include/linux/kcore.h        | 13 +++++++++++++
>>>  3 files changed, 28 insertions(+), 2 deletions(-)
>>
>> This also adds the KCORE_REMAP functionality, but isn't mentioned at all
>> in the Changelog.
>>
>> Still, looks OK I suppose,
> 
> I can add a note about that,
>  
>> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> 
> Thanks, giving it some more hours and will apply and try to test it.

Any update on this?

Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

[Arnaldo Carvalho de Melo]

Em Tue, Jul 17, 2018 at 11:54:30AM +0300, Adrian Hunter escreveu:
> On 06/06/18 16:19, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Jun 06, 2018 at 03:16:31PM +0200, Peter Zijlstra escreveu:
> >> On Wed, Jun 06, 2018 at 03:54:11PM +0300, Adrian Hunter wrote:
> >>> Without program headers for PTI entry trampoline pages, the trampoline
> >>> virtual addresses do not map to anything.
> >>>
> >>
> >>>
> >>> In addition, entry trampolines all map to the same page.  Represent that by
> >>> giving the corresponding program headers in kcore the same offset.
> >>>
> >>> This has the benefit that, when perf tools uses /proc/kcore as a source for
> >>> kernel object code, samples from different CPU trampolines are aggregated
> >>> together.  Note, such aggregation is normal for profiling i.e. people want
> >>> to profile the object code, not every different virtual address the object
> >>> code might be mapped to (across different processes for example).
> >>>
> >>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> >>> Acked-by: Andi Kleen <ak@linux.intel.com>
> >>> ---
> >>>  arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
> >>>  fs/proc/kcore.c              |  7 +++++--
> >>>  include/linux/kcore.h        | 13 +++++++++++++
> >>>  3 files changed, 28 insertions(+), 2 deletions(-)
> >>
> >> This also adds the KCORE_REMAP functionality, but isn't mentioned at all
> >> in the Changelog.
> >>
> >> Still, looks OK I suppose,
> > 
> > I can add a note about that,
> >  
> >> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > 
> > Thanks, giving it some more hours and will apply and try to test it.
> 
> Any update on this?

On the post-vacation pile, will get to it.

- Arnaldo

[tip:perf/urgent] kallsyms: Simplify update_iter_mod()

[tip-bot for Adrian Hunter]

Commit-ID:  b96679422007c3fa04625be14977904c27c722eb
Gitweb:     https://git.kernel.org/tip/b96679422007c3fa04625be14977904c27c722eb
Author:     Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Wed, 6 Jun 2018 15:54:09 +0300
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 14 Aug 2018 19:10:23 -0300

kallsyms: Simplify update_iter_mod()

The logic in update_iter_mod() is overcomplicated and gets worse every
time another get_ksymbol_* function is added.

In preparation for adding another get_ksymbol_* function, simplify logic
in update_iter_mod().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: (ftrace changes only) Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/1528289651-4113-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 kernel/kallsyms.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index a23e21ada81b..aa31aa07f2ef 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -506,27 +506,24 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 	}
 }
 
+/*
+ * The end position (last + 1) of each additional kallsyms section is recorded
+ * in iter->pos_..._end as each section is added, and so can be used to
+ * determine which get_ksymbol_...() function to call next.
+ */
 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 {
 	iter->pos = pos;
 
-	if (iter->pos_ftrace_mod_end > 0 &&
-	    iter->pos_ftrace_mod_end < iter->pos)
-		return get_ksymbol_bpf(iter);
-
-	if (iter->pos_mod_end > 0 &&
-	    iter->pos_mod_end < iter->pos) {
-		if (!get_ksymbol_ftrace_mod(iter))
-			return get_ksymbol_bpf(iter);
+	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
+	    get_ksymbol_mod(iter))
 		return 1;
-	}
 
-	if (!get_ksymbol_mod(iter)) {
-		if (!get_ksymbol_ftrace_mod(iter))
-			return get_ksymbol_bpf(iter);
-	}
+	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
+	    get_ksymbol_ftrace_mod(iter))
+		return 1;
 
-	return 1;
+	return get_ksymbol_bpf(iter);
 }
 
 /* Returns false if pos at or past end of file. */

[tip:perf/urgent] kallsyms, x86: Export addresses of PTI entry trampolines

[tip-bot for Alexander Shishkin]

Commit-ID:  d83212d5dd6761625fe87cc23016bbaa47303271
Gitweb:     https://git.kernel.org/tip/d83212d5dd6761625fe87cc23016bbaa47303271
Author:     Alexander Shishkin <alexander.shishkin@linux.intel.com>
AuthorDate: Wed, 6 Jun 2018 15:54:10 +0300
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 14 Aug 2018 19:12:29 -0300

kallsyms, x86: Export addresses of PTI entry trampolines

Currently, the addresses of PTI entry trampolines are not exported to
user space. Kernel profiling tools need these addresses to identify the
kernel code, so add a symbol and address for each CPU's PTI entry
trampoline.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/1528289651-4113-3-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 arch/x86/mm/cpu_entry_area.c | 23 +++++++++++++++++++++++
 kernel/kallsyms.c            | 28 +++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index b45f5aaefd74..fab49fd5190f 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -2,6 +2,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
+#include <linux/kallsyms.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/pgtable.h>
@@ -150,6 +151,28 @@ static void __init setup_cpu_entry_area(int cpu)
 	percpu_setup_debug_store(cpu);
 }
 
+#ifdef CONFIG_X86_64
+int arch_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+		     char *name)
+{
+	unsigned int cpu, ncpu = 0;
+
+	if (symnum >= num_possible_cpus())
+		return -EINVAL;
+
+	for_each_possible_cpu(cpu) {
+		if (ncpu++ >= symnum)
+			break;
+	}
+
+	*value = (unsigned long)&get_cpu_entry_area(cpu)->entry_trampoline;
+	*type = 't';
+	strlcpy(name, "__entry_SYSCALL_64_trampoline", KSYM_NAME_LEN);
+
+	return 0;
+}
+#endif
+
 static __init void setup_cpu_entry_area_ptes(void)
 {
 #ifdef CONFIG_X86_32
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index aa31aa07f2ef..02a0b01380d8 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -432,6 +432,7 @@ int sprint_backtrace(char *buffer, unsigned long address)
 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 struct kallsym_iter {
 	loff_t pos;
+	loff_t pos_arch_end;
 	loff_t pos_mod_end;
 	loff_t pos_ftrace_mod_end;
 	unsigned long value;
@@ -443,9 +444,29 @@ struct kallsym_iter {
 	int show_value;
 };
 
+int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
+			    char *type, char *name)
+{
+	return -EINVAL;
+}
+
+static int get_ksymbol_arch(struct kallsym_iter *iter)
+{
+	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
+				   &iter->value, &iter->type,
+				   iter->name);
+
+	if (ret < 0) {
+		iter->pos_arch_end = iter->pos;
+		return 0;
+	}
+
+	return 1;
+}
+
 static int get_ksymbol_mod(struct kallsym_iter *iter)
 {
-	int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
+	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 				     &iter->value, &iter->type,
 				     iter->name, iter->module_name,
 				     &iter->exported);
@@ -501,6 +522,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 	iter->nameoff = get_symbol_offset(new_pos);
 	iter->pos = new_pos;
 	if (new_pos == 0) {
+		iter->pos_arch_end = 0;
 		iter->pos_mod_end = 0;
 		iter->pos_ftrace_mod_end = 0;
 	}
@@ -515,6 +537,10 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 {
 	iter->pos = pos;
 
+	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
+	    get_ksymbol_arch(iter))
+		return 1;
+
 	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 	    get_ksymbol_mod(iter))
 		return 1;

[tip:perf/urgent] x86: Add entry trampolines to kcore

[tip-bot for Adrian Hunter]

Commit-ID:  6855dc41b24619c3d1de3dbd27dd0546b0e45272
Gitweb:     https://git.kernel.org/tip/6855dc41b24619c3d1de3dbd27dd0546b0e45272
Author:     Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Wed, 6 Jun 2018 15:54:11 +0300
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 14 Aug 2018 19:13:26 -0300

x86: Add entry trampolines to kcore

Without program headers for PTI entry trampoline pages, the trampoline
virtual addresses do not map to anything.

Example before:

 sudo gdb --quiet vmlinux /proc/kcore
 Reading symbols from vmlinux...done.
 [New process 1]
 Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.16.0 root=UUID=a6096b83-b763-4101-807e-f33daff63233'.
 #0  0x0000000000000000 in irq_stack_union ()
 (gdb) x /21ib 0xfffffe0000006000
    0xfffffe0000006000:  Cannot access memory at address 0xfffffe0000006000
 (gdb) quit

After:

 sudo gdb --quiet vmlinux /proc/kcore
 [sudo] password for ahunter:
 Reading symbols from vmlinux...done.
 [New process 1]
 Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.16.0-fix-4-00005-gd6e65a8b4072 root=UUID=a6096b83-b7'.
 #0  0x0000000000000000 in irq_stack_union ()
 (gdb) x /21ib 0xfffffe0000006000
    0xfffffe0000006000:  swapgs
    0xfffffe0000006003:  mov    %rsp,-0x3e12(%rip)        # 0xfffffe00000021f8
    0xfffffe000000600a:  xchg   %ax,%ax
    0xfffffe000000600c:  mov    %cr3,%rsp
    0xfffffe000000600f:  bts    $0x3f,%rsp
    0xfffffe0000006014:  and    $0xffffffffffffe7ff,%rsp
    0xfffffe000000601b:  mov    %rsp,%cr3
    0xfffffe000000601e:  mov    -0x3019(%rip),%rsp        # 0xfffffe000000300c
    0xfffffe0000006025:  pushq  $0x2b
    0xfffffe0000006027:  pushq  -0x3e35(%rip)        # 0xfffffe00000021f8
    0xfffffe000000602d:  push   %r11
    0xfffffe000000602f:  pushq  $0x33
    0xfffffe0000006031:  push   %rcx
    0xfffffe0000006032:  push   %rdi
    0xfffffe0000006033:  mov    $0xffffffff91a00010,%rdi
    0xfffffe000000603a:  callq  0xfffffe0000006046
    0xfffffe000000603f:  pause
    0xfffffe0000006041:  lfence
    0xfffffe0000006044:  jmp    0xfffffe000000603f
    0xfffffe0000006046:  mov    %rdi,(%rsp)
    0xfffffe000000604a:  retq
 (gdb) quit

In addition, entry trampolines all map to the same page.  Represent that
by giving the corresponding program headers in kcore the same offset.

This has the benefit that, when perf tools uses /proc/kcore as a source
for kernel object code, samples from different CPU trampolines are
aggregated together.  Note, such aggregation is normal for profiling
i.e. people want to profile the object code, not every different virtual
address the object code might be mapped to (across different processes
for example).

Notes by PeterZ:

This also adds the KCORE_REMAP functionality.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/1528289651-4113-4-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
 fs/proc/kcore.c              |  7 +++++--
 include/linux/kcore.h        | 13 +++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index fab49fd5190f..076ebdce9bd4 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -3,6 +3,7 @@
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
 #include <linux/kallsyms.h>
+#include <linux/kcore.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/pgtable.h>
@@ -14,6 +15,7 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage)
 #ifdef CONFIG_X86_64
 static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
 	[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
+static DEFINE_PER_CPU(struct kcore_list, kcore_entry_trampoline);
 #endif
 
 struct cpu_entry_area *get_cpu_entry_area(int cpu)
@@ -147,6 +149,14 @@ static void __init setup_cpu_entry_area(int cpu)
 
 	cea_set_pte(&get_cpu_entry_area(cpu)->entry_trampoline,
 		     __pa_symbol(_entry_trampoline), PAGE_KERNEL_RX);
+	/*
+	 * The cpu_entry_area alias addresses are not in the kernel binary
+	 * so they do not show up in /proc/kcore normally.  This adds entries
+	 * for them manually.
+	 */
+	kclist_add_remap(&per_cpu(kcore_entry_trampoline, cpu),
+			 _entry_trampoline,
+			 &get_cpu_entry_area(cpu)->entry_trampoline, PAGE_SIZE);
 #endif
 	percpu_setup_debug_store(cpu);
 }
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index e64ecb9f2720..00282f134336 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -383,8 +383,11 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
 		phdr->p_type	= PT_LOAD;
 		phdr->p_flags	= PF_R|PF_W|PF_X;
 		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
-		phdr->p_vaddr	= (size_t)m->addr;
-		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
+		if (m->type == KCORE_REMAP)
+			phdr->p_vaddr	= (size_t)m->vaddr;
+		else
+			phdr->p_vaddr	= (size_t)m->addr;
+		if (m->type == KCORE_RAM || m->type == KCORE_TEXT || m->type == KCORE_REMAP)
 			phdr->p_paddr	= __pa(m->addr);
 		else
 			phdr->p_paddr	= (elf_addr_t)-1;
diff --git a/include/linux/kcore.h b/include/linux/kcore.h
index 8de55e4b5ee9..bc088ef96358 100644
--- a/include/linux/kcore.h
+++ b/include/linux/kcore.h
@@ -12,11 +12,13 @@ enum kcore_type {
 	KCORE_VMEMMAP,
 	KCORE_USER,
 	KCORE_OTHER,
+	KCORE_REMAP,
 };
 
 struct kcore_list {
 	struct list_head list;
 	unsigned long addr;
+	unsigned long vaddr;
 	size_t size;
 	int type;
 };
@@ -36,11 +38,22 @@ struct vmcoredd_node {
 
 #ifdef CONFIG_PROC_KCORE
 extern void kclist_add(struct kcore_list *, void *, size_t, int type);
+static inline
+void kclist_add_remap(struct kcore_list *m, void *addr, void *vaddr, size_t sz)
+{
+	m->vaddr = (unsigned long)vaddr;
+	kclist_add(m, addr, sz, KCORE_REMAP);
+}
 #else
 static inline
 void kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 {
 }
+
+static inline
+void kclist_add_remap(struct kcore_list *m, void *addr, void *vaddr, size_t sz)
+{
+}
 #endif
 
 #endif /* _LINUX_KCORE_H */