diff options
| author | Denys Vlasenko <dvlasenk@redhat.com> | 2015-03-31 19:00:03 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-04-01 13:17:38 +0200 |
| commit | 4416c5a6dacdddd55378e7011f9c8720d2a7470f (patch) | |
| tree | f85909f26079047ccefe87f7a15d78bf6f59bd52 /arch | |
| parent | 55474c48b4726fd3914c1ec47fced0f931729979 (diff) | |
x86/asm/entry/64: Do not TRACE_IRQS fast SYSRET64 path
SYSRET code path has a small irq-off block.
On this code path, TRACE_IRQS_ON can't be called right before
interrupts are enabled for real, we can't clobber registers
there. So current code does it earlier, in a safe place.
But with this, TRACE_IRQS_OFF/ON frames just two fast
instructions, which is ridiculous: now most of irq-off block is
_outside_ of the framing.
Do the same thing that we do on SYSCALL entry: do not track this
irq-off block, it is very small to ever cause noticeable irq
latency.
Be careful: make sure that "jnz int_ret_from_sys_call_irqs_off"
now does invoke TRACE_IRQS_OFF - move
int_ret_from_sys_call_irqs_off label before TRACE_IRQS_OFF.
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/1427821211-25099-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 6f251a5ee1dc..f6e37de02ba7 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -269,8 +269,11 @@ system_call_fastpath: * Has incompletely filled pt_regs. */ LOCKDEP_SYS_EXIT + /* + * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, + * it is too small to ever cause noticeable irq latency. + */ DISABLE_INTERRUPTS(CLBR_NONE) - TRACE_IRQS_OFF /* * We must check ti flags with interrupts (or at least preemption) @@ -284,10 +287,7 @@ system_call_fastpath: jnz int_ret_from_sys_call_irqs_off /* Go to the slow path */ CFI_REMEMBER_STATE - /* - * sysretq will re-enable interrupts: - */ - TRACE_IRQS_ON + RESTORE_C_REGS_EXCEPT_RCX_R11 movq RIP(%rsp),%rcx CFI_REGISTER rip,rcx @@ -298,6 +298,7 @@ system_call_fastpath: * 64bit SYSRET restores rip from rcx, * rflags from r11 (but RF and VM bits are forced to 0), * cs and ss are loaded from MSRs. + * Restoration of rflags re-enables interrupts. */ USERGS_SYSRET64 @@ -346,8 +347,8 @@ tracesys_phase2: */ GLOBAL(int_ret_from_sys_call) DISABLE_INTERRUPTS(CLBR_NONE) +int_ret_from_sys_call_irqs_off: /* jumps come here from the irqs-off SYSRET path */ TRACE_IRQS_OFF -int_ret_from_sys_call_irqs_off: movl $_TIF_ALLWORK_MASK,%edi /* edi: mask to check */ GLOBAL(int_with_check) |