diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-06-14 23:15:58 +0200 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2022-06-27 10:33:59 +0200 |
| commit | bf5835bcdb9635c97f85120dba9bfa21e111130f (patch) | |
| tree | c5d11e696c13f6a27b6fe1703f293b6e6b6655d6 /arch/x86 | |
| parent | 6ad0ad2bf8a67e27d1f9d006a1dabb0e1c360cc3 (diff) | |
intel_idle: Disable IBRS during long idle
Having IBRS enabled while the SMT sibling is idle unnecessarily slows
down the running sibling. OTOH, disabling IBRS around idle takes two
MSR writes, which will increase the idle latency.
Therefore, only disable IBRS around deeper idle states. Shallow idle
states are bounded by the tick in duration, since NOHZ is not allowed
for them by virtue of their short target residency.
Only do this for mwait-driven idle, since that keeps interrupts disabled
across idle, which makes disabling IBRS vs IRQ-entry a non-issue.
Note: C6 is a random threshold, most importantly C1 probably shouldn't
disable IBRS, benchmarking needed.
Suggested-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/nospec-branch.h | 1 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/bugs.c | 6 |
2 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index e14046daa7ba..ce1acb557162 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -255,6 +255,7 @@ static inline void indirect_branch_prediction_barrier(void) /* The Intel SPEC CTRL MSR base value cache */ extern u64 x86_spec_ctrl_base; extern void write_spec_ctrl_current(u64 val, bool force); +extern u64 spec_ctrl_current(void); /* * With retpoline, we must use IBRS to restrict branch prediction diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 05f29db9473b..00e9c769ce0b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -79,6 +79,12 @@ void write_spec_ctrl_current(u64 val, bool force) wrmsrl(MSR_IA32_SPEC_CTRL, val); } +u64 spec_ctrl_current(void) +{ + return this_cpu_read(x86_spec_ctrl_current); +} +EXPORT_SYMBOL_GPL(spec_ctrl_current); + /* * The vendor and possibly platform specific bits which can be modified in * x86_spec_ctrl_base. |