Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying mappings

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Mon, 7 Feb 2011, Stefano Stabellini wrote:
> On Sun, 6 Feb 2011, Yinghai Lu wrote:
> > On 02/05/2011 11:30 PM, H. Peter Anvin wrote:
> > > On 02/05/2011 11:02 PM, Yinghai Lu wrote:
> > >> why not just move calling cleanup_highmap down?
> > >>
> > >> something like attached patch.
> > > 
> > > This patch looks very clean and looks on the surface of it like it is
> > > removing some ugly ad hoc code, but (as always) it needs a description
> > > about the problem it solves and why it is correct.
> > 
> > Sure.
> > 
> > 
> > Jeremy and xen guys, can you please check if it works well with xen ?
> > 
> 
> Actually this patch makes things worse on xen, because before
> cleanup_highmap() wasn't called at all on xen (on purpose) and now it
> is, fully destroying all the mappings we have at _end.
> 
> Can we add a check on memblock reserved regions in cleanup_highmap()?

In case you are wondering how Yinghai Lu's patch would look like with
the added check, here it is:


diff --git a/arch/x86/include/asm/memblock.h b/arch/x86/include/asm/memblock.h
index 19ae14b..184f778 100644
--- a/arch/x86/include/asm/memblock.h
+++ b/arch/x86/include/asm/memblock.h
@@ -3,6 +3,7 @@
 
 #define ARCH_DISCARD_MEMBLOCK
 
+bool memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align);
 u64 memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align);
 void memblock_x86_to_bootmem(u64 start, u64 end);
 
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 975f709..28686b6 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -165,7 +165,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; }
 #define __swp_entry_to_pte(x)		((pte_t) { .pte = (x).val })
 
 extern int kern_addr_valid(unsigned long addr);
-extern void cleanup_highmap(void);
+extern void cleanup_highmap(unsigned long end);
 
 #define HAVE_ARCH_UNMAPPED_AREA
 #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 2d2673c..5655c22 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -77,9 +77,6 @@ void __init x86_64_start_kernel(char * real_mode_data)
 	/* Make NULL pointers segfault */
 	zap_identity_mappings();
 
-	/* Cleanup the over mapped high alias */
-	cleanup_highmap();
-
 	max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
 
 	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d3cfe26..91afde6 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -297,6 +297,9 @@ static void __init init_gbpages(void)
 static inline void init_gbpages(void)
 {
 }
+static void __init cleanup_highmap(unsigned long end)
+{
+}
 #endif
 
 static void __init reserve_brk(void)
@@ -922,6 +925,9 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	reserve_brk();
 
+	/* Cleanup the over mapped high alias after _brk_end*/
+	cleanup_highmap(_brk_end);
+
 	memblock.current_limit = get_max_mapped();
 	memblock_x86_fill();
 
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 947f42a..f13ff3a 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -279,25 +279,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 	load_cr3(swapper_pg_dir);
 #endif
 
-#ifdef CONFIG_X86_64
-	if (!after_bootmem && !start) {
-		pud_t *pud;
-		pmd_t *pmd;
-
-		mmu_cr4_features = read_cr4();
-
-		/*
-		 * _brk_end cannot change anymore, but it and _end may be
-		 * located on different 2M pages. cleanup_highmap(), however,
-		 * can only consider _end when it runs, so destroy any
-		 * mappings beyond _brk_end here.
-		 */
-		pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
-		pmd = pmd_offset(pud, _brk_end - 1);
-		while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
-			pmd_clear(pmd);
-	}
-#endif
 	__flush_tlb_all();
 
 	if (!after_bootmem && e820_table_end > e820_table_start)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 71a5929..028c49e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -297,18 +297,26 @@ void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
  * rounded up to the 2MB boundary. This catches the invalid pmds as
  * well, as they are located before _text:
  */
-void __init cleanup_highmap(void)
+void __init cleanup_highmap(unsigned long end)
 {
 	unsigned long vaddr = __START_KERNEL_map;
-	unsigned long end = roundup((unsigned long)_end, PMD_SIZE) - 1;
 	pmd_t *pmd = level2_kernel_pgt;
 	pmd_t *last_pmd = pmd + PTRS_PER_PMD;
+	u64 size, addrp;
+	bool changed;
+
+	end = roundup(end, PMD_SIZE) - 1;
 
 	for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
 		if (pmd_none(*pmd))
 			continue;
-		if (vaddr < (unsigned long) _text || vaddr > end)
-			set_pmd(pmd, __pmd(0));
+		if (vaddr < (unsigned long) _text || vaddr > end) {
+			addrp = __pa(vaddr);
+			size = PMD_SIZE;
+			changed = memblock_check_reserved_size(&addrp, &size, PMD_SIZE);
+			if (!changed && size)
+				set_pmd(pmd, __pmd(0));
+		}
 	}
 }
 
diff --git a/arch/x86/mm/memblock.c b/arch/x86/mm/memblock.c
index aa11693..fac21d4 100644
--- a/arch/x86/mm/memblock.c
+++ b/arch/x86/mm/memblock.c
@@ -8,7 +8,7 @@
 #include <linux/range.h>
 
 /* Check for already reserved areas */
-static bool __init check_with_memblock_reserved_size(u64 *addrp, u64 *sizep, u64 align)
+bool __init memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align)
 {
 	struct memblock_region *r;
 	u64 addr = *addrp, last;
@@ -59,7 +59,7 @@ u64 __init memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align)
 		if (addr >= ei_last)
 			continue;
 		*sizep = ei_last - addr;
-		while (check_with_memblock_reserved_size(&addr, sizep, align))
+		while (memblock_check_reserved_size(&addr, sizep, align))
 			;
 
 		if (*sizep)