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| author |   Peter Zijlstra <peterz@infradead.org> | 2022-06-14 23:15:54 +0200 |
|---|---|---|
| committer |   Borislav Petkov <bp@suse.de> | 2022-06-27 10:33:59 +0200 |
| commit | c779bc1a9002fa474175b80e72b85c9bf628abb0 (patch) | |
| tree | e79fbab2ca5f15aad4a76200cd56c6ae899dfd67 /arch/x86 | |
| parent | x86/entry: Add kernel IBRS implementation (diff) | |
| download | linux-dev-c779bc1a9002fa474175b80e72b85c9bf628abb0.tar.xz linux-dev-c779bc1a9002fa474175b80e72b85c9bf628abb0.zip | |
x86/bugs: Optimize SPEC_CTRL MSR writes
When changing SPEC_CTRL for user control, the WRMSR can be delayed
until return-to-user when KERNEL_IBRS has been enabled.
This avoids an MSR write during context switch.
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 | 2 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/bugs.c | 18 | ||||
| -rw-r--r-- | arch/x86/kernel/process.c | 2 |
3 files changed, 14 insertions, 8 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index bac243da5130..b6abf0c6b41d 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -253,7 +253,7 @@ 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); +extern void write_spec_ctrl_current(u64 val, bool force); /* * 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 ce7435593c3e..8f7c8dfbdbb4 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -63,13 +63,19 @@ static DEFINE_MUTEX(spec_ctrl_mutex); * Keep track of the SPEC_CTRL MSR value for the current task, which may differ * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update(). */ -void write_spec_ctrl_current(u64 val) +void write_spec_ctrl_current(u64 val, bool force) { if (this_cpu_read(x86_spec_ctrl_current) == val) return; this_cpu_write(x86_spec_ctrl_current, val); - wrmsrl(MSR_IA32_SPEC_CTRL, val); + + /* + * When KERNEL_IBRS this MSR is written on return-to-user, unless + * forced the update can be delayed until that time. + */ + if (force || !cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) + wrmsrl(MSR_IA32_SPEC_CTRL, val); } /* @@ -1297,7 +1303,7 @@ static void __init spectre_v2_select_mitigation(void) if (spectre_v2_in_eibrs_mode(mode)) { /* Force it so VMEXIT will restore correctly */ x86_spec_ctrl_base |= SPEC_CTRL_IBRS; - write_spec_ctrl_current(x86_spec_ctrl_base); + write_spec_ctrl_current(x86_spec_ctrl_base, true); } switch (mode) { @@ -1352,7 +1358,7 @@ static void __init spectre_v2_select_mitigation(void) static void update_stibp_msr(void * __unused) { - write_spec_ctrl_current(x86_spec_ctrl_base); + write_spec_ctrl_current(x86_spec_ctrl_base, true); } /* Update x86_spec_ctrl_base in case SMT state changed. */ @@ -1595,7 +1601,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void) x86_amd_ssb_disable(); } else { x86_spec_ctrl_base |= SPEC_CTRL_SSBD; - write_spec_ctrl_current(x86_spec_ctrl_base); + write_spec_ctrl_current(x86_spec_ctrl_base, true); } } @@ -1846,7 +1852,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) void x86_spec_ctrl_setup_ap(void) { if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) - write_spec_ctrl_current(x86_spec_ctrl_base); + write_spec_ctrl_current(x86_spec_ctrl_base, true); if (ssb_mode == SPEC_STORE_BYPASS_DISABLE) x86_amd_ssb_disable(); diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 05611f66d013..d456ce21c255 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -600,7 +600,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp, } if (updmsr) - write_spec_ctrl_current(msr); + write_spec_ctrl_current(msr, false); } static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk) |