linux-kernel - [PATCH 2/4] x86/asm/entry/32: Update "interrupt off" comments

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Message-Id: <1427452582-21624-2-git-send-email-dvlasenk@redhat.com>
Date:	Fri, 27 Mar 2015 11:36:20 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] x86/asm/entry/32: Update "interrupt off" comments

The existing comment has proven to be not very clear.
Replace it with comment similar to one we now have in 64-bit syscall
entry point. (Three instances, one per 32-bit syscall entry).

In 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: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.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
-- 
1.8.1.4

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