Elide the OSVW variable updates if the current CPU's set of errata are a subset of the errata tracked in the global values, i.e. if no update is needed. There's no danger of under-reporting errata due to bailing early as KVM is purely reducing the set of "known fixed" errata. I.e. a racing update on a different CPU with _more_ errata doesn't change anything if the current CPU has the same or fewer errata relative to the status quo. If another CPU is writing osvw_len, then "len" is guaranteed to be larger than the new osvw_len and so the osvw_len update would be skipped anyways. If another CPU is setting new bits in osvw_status, then "status" is guaranteed to be a subset of the new osvw_status and the bitwise-OR would be an effective nop anyways. Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/svm.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index d3f0cc5632d1..152c56762b26 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -420,7 +420,6 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu) static void svm_init_os_visible_workarounds(void) { u64 len, status; - int err; /* * Get OS-Visible Workarounds (OSVW) bits. @@ -449,20 +448,19 @@ static void svm_init_os_visible_workarounds(void) return; } - err = native_read_msr_safe(MSR_AMD64_OSVW_ID_LENGTH, &len); - if (!err) - err = native_read_msr_safe(MSR_AMD64_OSVW_STATUS, &status); + if (native_read_msr_safe(MSR_AMD64_OSVW_ID_LENGTH, &len) || + native_read_msr_safe(MSR_AMD64_OSVW_STATUS, &status)) + len = status = 0; + + if (status == READ_ONCE(osvw_status) && len >= READ_ONCE(osvw_len)) + return; guard(spinlock)(&osvw_lock); - if (err) { - osvw_status = osvw_len = 0; - } else { - if (len < osvw_len) - osvw_len = len; - osvw_status |= status; - osvw_status &= (1ULL << osvw_len) - 1; - } + if (len < osvw_len) + osvw_len = len; + osvw_status |= status; + osvw_status &= (1ULL << osvw_len) - 1; } static bool __kvm_is_svm_supported(void) -- 2.52.0.rc1.455.g30608eb744-goog