On Wed, Oct 7, 2015 at 10:39 AM, Denys Vlasenko <dvlas...@redhat.com> wrote: > On 10/06/2015 02:47 AM, Andy Lutomirski wrote: >> We eventually want to make it all the way into C code before >> enabling interrupts. We need to rework our flags handling slightly >> to delay enabling interrupts. >> >> Signed-off-by: Andy Lutomirski <l...@kernel.org> >> --- >> arch/x86/entry/entry_64_compat.S | 30 ++++++++++++++++++++++-------- >> 1 file changed, 22 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64_compat.S >> b/arch/x86/entry/entry_64_compat.S >> index aa76864a8a6b..1432d60a1f4a 100644 >> --- a/arch/x86/entry/entry_64_compat.S >> +++ b/arch/x86/entry/entry_64_compat.S >> @@ -58,14 +58,9 @@ ENDPROC(native_usergs_sysret32) >> * with the int 0x80 path. >> */ >> ENTRY(entry_SYSENTER_compat) >> - /* >> - * 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. >> - */ >> + /* Interrupts are off on entry. */ >> SWAPGS_UNSAFE_STACK >> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp >> - ENABLE_INTERRUPTS(CLBR_NONE) >> >> /* Zero-extending 32-bit regs, do not remove */ >> movl %ebp, %ebp >> @@ -76,7 +71,16 @@ ENTRY(entry_SYSENTER_compat) >> /* Construct struct pt_regs on stack */ >> pushq $__USER32_DS /* pt_regs->ss */ >> pushq %rbp /* pt_regs->sp */ >> - pushfq /* pt_regs->flags */ >> + >> + /* >> + * Push flags. This is nasty. First, interrupts are currently >> + * off, but we need pt_regs->flags to have IF set. Second, even >> + * if TF was set when SYSENTER started, it's clear by now. We fix >> + * that later using TIF_SINGLESTEP. >> + */ >> + pushfq /* pt_regs->flags (except IF = 0) */ >> + orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */ > > The sequence of "push + insn_using_rsp" is a bit slow > on most CPUs because stack engine (the machinery which makes > consecutive pushes fast) needs syncronizing with register file. > > It may be better to move the ORL insn here: > > push, push, push > cld > sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */ > + orl $X86_EFLAGS_IF, EFLAGS(%rsp) /* Fix saved flags to have .IF > = 1 */ > > where we already eat that penalty. > >
I'll benchmark this and, if it's a win, I'll tack it on to the end of the series. -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
