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 <dvlas...@redhat.com>
CC: Linus Torvalds <torva...@linux-foundation.org>
CC: Steven Rostedt <rost...@goodmis.org>
CC: Ingo Molnar <mi...@kernel.org>
CC: Borislav Petkov <b...@alien8.de>
CC: "H. Peter Anvin" <h...@zytor.com>
CC: Andy Lutomirski <l...@amacapital.net>
CC: Oleg Nesterov <o...@redhat.com>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Alexei Starovoitov <a...@plumgrid.com>
CC: Will Drewry <w...@chromium.org>
CC: Kees Cook <keesc...@chromium.org>
CC: x...@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/kernel/entry_64.S | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 6f251a5..f6e37de 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)
--
1.8.1.4
--
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