diff options
| author | Sean Christopherson <seanjc@google.com> | 2023-07-28 18:15:51 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2023-08-03 17:16:29 -0700 |
| commit | 229725acfaea0dd81f245aec40986dc766de40fa (patch) | |
| tree | fa50aa1c16a6a0e44a3e0e2850cac03b5ebd3f1f /arch/x86/kvm/svm/svm.c | |
| parent | c0dc39bd2c584879748dfd1321f8541d1cbeb9b8 (diff) | |
KVM: SVM: Clean up preemption toggling related to MSR_AMD64_TSC_RATIO
Explicitly disable preemption when writing MSR_AMD64_TSC_RATIO only in the
"outer" helper, as all direct callers of the "inner" helper now run with
preemption already disabled. And that isn't a coincidence, as the outer
helper requires a vCPU and is intended to be used when modifying guest
state and/or emulating guest instructions, which are typically done with
preemption enabled.
Direct use of the inner helper should be extremely limited, as the only
time KVM should modify MSR_AMD64_TSC_RATIO without a vCPU is when
sanitizing the MSR for a specific pCPU (currently done when {en,dis}abling
disabling SVM). The other direct caller is svm_prepare_switch_to_guest(),
which does have a vCPU, but is a one-off special case: KVM is about to
enter the guest on a specific pCPU and thus must have preemption disabled.
Link: https://lore.kernel.org/r/20230729011608.1065019-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch/x86/kvm/svm/svm.c')
| -rw-r--r-- | arch/x86/kvm/svm/svm.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 7217f7532df9..b66af2966ec7 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -569,15 +569,11 @@ static int svm_check_processor_compat(void) static void __svm_write_tsc_multiplier(u64 multiplier) { - preempt_disable(); - if (multiplier == __this_cpu_read(current_tsc_ratio)) - goto out; + return; wrmsrl(MSR_AMD64_TSC_RATIO, multiplier); __this_cpu_write(current_tsc_ratio, multiplier); -out: - preempt_enable(); } static inline void kvm_cpu_svm_disable(void) @@ -1152,7 +1148,9 @@ static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset) void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier) { + preempt_disable(); __svm_write_tsc_multiplier(multiplier); + preempt_enable(); } /* Evaluate instruction intercepts that depend on guest CPUID features. */ |