linux-kernel - [PATCH 2/6] x86/entry: Simplify entry_INT80

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Date:   Fri, 06 May 2022 14:14:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        jpoimboe@...hat.com, brgerst@...il.com, jiangshanlai@...il.com,
        Andrew.Cooper3@...rix.com, mark.rutland@....com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>
Subject: [PATCH 2/6] x86/entry: Simplify entry_INT80_compat()

From: Linus Torvalds <torvalds@...ux-foundation.org>

Instead of playing silly games with rdi, use rax for simpler and more
consistent code.

Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[peterz: Changelog and fix off-by-one in offsets]
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/entry/entry_64_compat.S |   19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -362,26 +362,25 @@ SYM_CODE_START(entry_INT80_compat)
 
 	/* switch to thread stack expects orig_ax and rdi to be pushed */
 	pushq	%rax			/* pt_regs->orig_ax */
-	pushq	%rdi			/* pt_regs->di */
 
 	/* Need to switch before accessing the thread stack. */
-	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
+	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
 
 	/* In the Xen PV case we already run on the thread stack. */
 	ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
 
-	movq	%rsp, %rdi
+	movq	%rsp, %rax
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
-	pushq	6*8(%rdi)		/* regs->ss */
-	pushq	5*8(%rdi)		/* regs->rsp */
-	pushq	4*8(%rdi)		/* regs->eflags */
-	pushq	3*8(%rdi)		/* regs->cs */
-	pushq	2*8(%rdi)		/* regs->ip */
-	pushq	1*8(%rdi)		/* regs->orig_ax */
-	pushq	(%rdi)			/* pt_regs->di */
+	pushq	5*8(%rax)		/* regs->ss */
+	pushq	4*8(%rax)		/* regs->rsp */
+	pushq	3*8(%rax)		/* regs->eflags */
+	pushq	2*8(%rax)		/* regs->cs */
+	pushq	1*8(%rax)		/* regs->ip */
+	pushq	0*8(%rax)		/* regs->orig_ax */
 .Lint80_keep_stack:
 
+	pushq	%rdi			/* pt_regs->di */
 	pushq	%rsi			/* pt_regs->si */
 	xorl	%esi, %esi		/* nospec   si */
 	pushq	%rdx			/* pt_regs->dx */