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>

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 5d2641ce995769e21825c5e0359205024bfdd5c3..7502ff0b938e0296320b839d09c4857d48248225 100644 (file)
--- 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