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Message-Id: <1427303896-24023-2-git-send-email-dvlasenk@redhat.com> Date: Wed, 25 Mar 2015 18:18:14 +0100 From: Denys Vlasenko <dvlasenk@...hat.com> To: Ingo Molnar <mingo@...nel.org> Cc: Denys Vlasenko <dvlasenk@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...capital.net>, Oleg Nesterov <oleg@...hat.com>, Frederic Weisbecker <fweisbec@...il.com>, Alexei Starovoitov <ast@...mgrid.com>, Will Drewry <wad@...omium.org>, Kees Cook <keescook@...omium.org>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: [PATCH 2/4] 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@...hat.com> CC: Linus Torvalds <torvalds@...ux-foundation.org> CC: Steven Rostedt <rostedt@...dmis.org> CC: Ingo Molnar <mingo@...nel.org> CC: Borislav Petkov <bp@...en8.de> CC: "H. Peter Anvin" <hpa@...or.com> CC: Andy Lutomirski <luto@...capital.net> CC: Oleg Nesterov <oleg@...hat.com> CC: Frederic Weisbecker <fweisbec@...il.com> CC: Alexei Starovoitov <ast@...mgrid.com> CC: Will Drewry <wad@...omium.org> CC: Kees Cook <keescook@...omium.org> CC: x86@...nel.org CC: linux-kernel@...r.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 40f7760..11b7339 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -268,8 +268,11 @@ 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) @@ -283,10 +286,7 @@ 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 @@ -297,6 +297,7 @@ 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 @@ -345,8 +346,8 @@ tracesys_phase2: */ GLOBAL(int_ret_from_sys_call) DISABLE_INTERRUPTS(CLBR_NONE) - TRACE_IRQS_OFF int_ret_from_sys_call_irqs_off: + TRACE_IRQS_OFF movl $_TIF_ALLWORK_MASK,%edi /* edi: mask to check */ GLOBAL(int_with_check) -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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