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Groups > linux.kernel > #1580381
| From | Kyle Huey <me@kylehuey.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v2 2/3] x86/process: Correct and optimize TIF_BLOCKSTEP switch |
| Date | 2017-02-14 09:20 +0100 |
| Message-ID | <taGv8-7K9-13@gated-at.bofh.it> (permalink) |
| References | <taGv7-7K9-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Because the MSR is "highly magical", reset DEBUGCTLMSR_BTF on every task
switch in or out of a task that uses TIF_BLOCKSTEP, even if both tasks
have TIF_BLOCKSTEP set. Avoid branching within the TIF_BLOCKSTEP case
and evaluating boot_cpu_data twice in kernels without
CONFIG_X86_DEBUGCTLMSR.
x86_64: arch/x86/kernel/process.o
text data bss dec hex
3024 8577 16 11617 2d61 Before
3008 8577 16 11601 2d51 After
i386: No change
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kyle Huey <khuey@kylehuey.com>
---
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/kernel/process.c | 12 ++++++------
2 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 710273c617b8..a8997a7b4e74 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -127,6 +127,7 @@
/* DEBUGCTLMSR bits (others vary by model): */
#define DEBUGCTLMSR_LBR (1UL << 0) /* last branch recording */
+#define _DEBUGCTLMSR_BTF 1
#define DEBUGCTLMSR_BTF (1UL << 1) /* single-step on branches */
#define DEBUGCTLMSR_TR (1UL << 6)
#define DEBUGCTLMSR_BTS (1UL << 7)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 01ef6f63d5fb..5dd08328108e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -209,13 +209,13 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
propagate_user_return_notify(prev_p, next_p);
- if ((tifp ^ tifn) & _TIF_BLOCKSTEP) {
- unsigned long debugctl = get_debugctlmsr();
-
+ if ((tifp & _TIF_BLOCKSTEP || tifn & _TIF_BLOCKSTEP) &&
+ arch_has_block_step()) {
+ unsigned long debugctl;
+ rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
debugctl &= ~DEBUGCTLMSR_BTF;
- if (tifn & _TIF_BLOCKSTEP)
- debugctl |= DEBUGCTLMSR_BTF;
- update_debugctlmsr(debugctl);
+ debugctl |= (tifn & _TIF_BLOCKSTEP) >> TIF_BLOCKSTEP << _DEBUGCTLMSR_BTF;
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
}
if ((tifp ^ tifn) & _TIF_NOTSC) {
--
2.11.0
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[PATCH v2 2/3] x86/process: Correct and optimize TIF_BLOCKSTEP switch Kyle Huey <me@kylehuey.com> - 2017-02-14 09:20 +0100
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