linux-kernel - [tip:x86/asm] x86/asm/entry/32: Update "interrupt off" comments

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Message-ID: <tip-a232e3d558eef421fbb539ede5483dfb668e38f2@git.kernel.org>
Date:	Sat, 28 Mar 2015 01:39:55 -0700
From:	tip-bot for Denys Vlasenko <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, torvalds@...ux-foundation.org,
	rostedt@...dmis.org, bp@...en8.de, fweisbec@...il.com,
	ast@...mgrid.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	luto@...capital.net, keescook@...omium.org, mingo@...nel.org,
	dvlasenk@...hat.com, oleg@...hat.com, wad@...omium.org
Subject: [tip:x86/asm] x86/asm/entry/32: Update "interrupt off" comments

Commit-ID:  a232e3d558eef421fbb539ede5483dfb668e38f2
Gitweb:     http://git.kernel.org/tip/a232e3d558eef421fbb539ede5483dfb668e38f2
Author:     Denys Vlasenko <dvlasenk@...hat.com>
AuthorDate: Fri, 27 Mar 2015 11:36:20 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 27 Mar 2015 12:27:57 +0100

x86/asm/entry/32: Update "interrupt off" comments

The existing comment has proven to be not very clear.

Replace it with a comment similar to the one we now have in the 64-bit
syscall entry point. (Three instances, one per 32-bit syscall entry).

In the INT80 entry point's CFI annotations, replace mysterious
expressions with numric constants. In this case, raw numbers
look more understandable.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Will Drewry <wad@...omium.org>
Link: http://lkml.kernel.org/r/1427452582-21624-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/ia32/ia32entry.S | 45 +++++++++++++++++++++++++++------------------
 1 file changed, 27 insertions(+), 18 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 5d2641c..7502ff0 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -112,13 +112,16 @@ ENTRY(ia32_sysenter_target)
 	CFI_SIGNAL_FRAME
 	CFI_DEF_CFA	rsp,0
 	CFI_REGISTER	rsp,rbp
-	SWAPGS_UNSAFE_STACK
-	movq	PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
+
 	/*
-	 * No need to follow this irqs on/off section: the syscall
-	 * disabled irqs, here we enable it straight after entry:
+	 * Interrupts are off on entry.
+	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
+	 * it is too small to ever cause noticeable irq latency.
 	 */
+	SWAPGS_UNSAFE_STACK
+	movq	PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
 	ENABLE_INTERRUPTS(CLBR_NONE)
+
 	/* Construct iret frame (ss,rsp,rflags,cs,rip) */
  	movl	%ebp,%ebp		/* zero extension */
 	pushq_cfi $__USER32_DS
@@ -314,15 +317,18 @@ ENTRY(ia32_cstar_target)
 	CFI_DEF_CFA	rsp,0
 	CFI_REGISTER	rip,rcx
 	/*CFI_REGISTER	rflags,r11*/
+
+	/*
+	 * Interrupts are off on entry.
+	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
+	 * it is too small to ever cause noticeable irq latency.
+	 */
 	SWAPGS_UNSAFE_STACK
 	movl	%esp,%r8d
 	CFI_REGISTER	rsp,r8
 	movq	PER_CPU_VAR(kernel_stack),%rsp
-	/*
-	 * No need to follow this irqs on/off section: the syscall
-	 * disabled irqs and here we enable it straight after entry:
-	 */
 	ENABLE_INTERRUPTS(CLBR_NONE)
+
 	ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */
 	SAVE_C_REGS_EXCEPT_RCX_R891011
 	movl 	%eax,%eax	/* zero extension */
@@ -449,19 +455,22 @@ ia32_badarg:
 ENTRY(ia32_syscall)
 	CFI_STARTPROC32	simple
 	CFI_SIGNAL_FRAME
-	CFI_DEF_CFA	rsp,SS+8-RIP
-	/*CFI_REL_OFFSET	ss,SS-RIP*/
-	CFI_REL_OFFSET	rsp,RSP-RIP
-	/*CFI_REL_OFFSET	rflags,EFLAGS-RIP*/
-	/*CFI_REL_OFFSET	cs,CS-RIP*/
-	CFI_REL_OFFSET	rip,RIP-RIP
-	PARAVIRT_ADJUST_EXCEPTION_FRAME
-	SWAPGS
+	CFI_DEF_CFA	rsp,5*8
+	/*CFI_REL_OFFSET	ss,4*8 */
+	CFI_REL_OFFSET	rsp,3*8
+	/*CFI_REL_OFFSET	rflags,2*8 */
+	/*CFI_REL_OFFSET	cs,1*8 */
+	CFI_REL_OFFSET	rip,0*8
+
 	/*
-	 * No need to follow this irqs on/off section: the syscall
-	 * disabled irqs and here we enable it straight after entry:
+	 * Interrupts are off on entry.
+	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
+	 * it is too small to ever cause noticeable irq latency.
 	 */
+	PARAVIRT_ADJUST_EXCEPTION_FRAME
+	SWAPGS
 	ENABLE_INTERRUPTS(CLBR_NONE)
+
 	movl %eax,%eax
 	pushq_cfi %rax		/* store orig_ax */
 	cld
--
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