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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@redhat.com>
AuthorDate: Fri, 27 Mar 2015 11:36:20 +0100
Committer: Ingo Molnar <mingo@kernel.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@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1427452582-21624-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@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

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