[PATCH V6 44/49] x86/sev: Add and use ist_vc_switch_off_ist()

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <laijs@linux.alibaba.com>

ist_vc_switch_off_ist() is the same as vc_switch_off_ist(), but it is
called without CR3 or gsbase fixed.  It has to call ist_paranoid_entry()
by its own.

It is prepared for using C code for the other part of identry_vc and
remove ASM paranoid_entry() and paranoid_exit().

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S    | 20 ++++++++++----------
 arch/x86/include/asm/traps.h |  3 ++-
 arch/x86/kernel/traps.c      | 14 +++++++++++++-
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 5a9738218722..b18df736b981 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -515,26 +515,26 @@ SYM_CODE_START(\asmsym)
 	testb	$3, CS(%rsp)
 	jnz	.Lfrom_usermode_switch_stack_\@
 
-	/*
-	 * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
-	 * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
-	 */
-	call	paranoid_entry
-
-	UNWIND_HINT_REGS
-
 	/*
 	 * Switch off the IST stack to make it free for nested exceptions. The
-	 * vc_switch_off_ist() function will switch back to the interrupted
+	 * ist_vc_switch_off_ist() function will switch back to the interrupted
 	 * stack if it is safe to do so. If not it switches to the VC fall-back
 	 * stack.
 	 */
 	movq	%rsp, %rdi		/* pt_regs pointer */
-	call	vc_switch_off_ist
+	call	ist_vc_switch_off_ist
 	movq	%rax, %rsp		/* Switch to new stack */
 
 	UNWIND_HINT_REGS
 
+	/*
+	 * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
+	 * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
+	 */
+	call	paranoid_entry
+
+	UNWIND_HINT_REGS
+
 	/* Update pt_regs */
 	movq	ORIG_RAX(%rsp), %rsi	/* get error code into 2nd argument*/
 	movq	$-1, ORIG_RAX(%rsp)	/* no syscall to restart */
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 686461ac9803..1aefc081d763 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -16,7 +16,8 @@ asmlinkage __visible notrace
 struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs);
 asmlinkage __visible notrace struct pt_regs *error_entry(struct pt_regs *eregs);
 void __init trap_init(void);
-asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *eregs);
+asmlinkage __visible __entry_text
+struct pt_regs *ist_vc_switch_off_ist(struct pt_regs *eregs);
 #endif
 
 #ifdef CONFIG_X86_F00F_BUG
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4e9d306f313c..1a84587cb4c7 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -717,7 +717,7 @@ asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs)
 }
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
-asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *regs)
+static noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *regs)
 {
 	unsigned long sp, *stack;
 	struct stack_info info;
@@ -757,6 +757,18 @@ asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *r
 
 	return regs_ret;
 }
+
+asmlinkage __visible __entry_text
+struct pt_regs *ist_vc_switch_off_ist(struct pt_regs *regs)
+{
+	unsigned long cr3, gsbase;
+
+	ist_paranoid_entry(&cr3, &gsbase);
+	regs = vc_switch_off_ist(regs);
+	ist_paranoid_exit(cr3, gsbase);
+
+	return regs;
+}
 #endif
 
 asmlinkage __visible noinstr
-- 
2.19.1.6.gb485710b