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KVM: x86: Apply TSX_CTRL_CPUID_CLEAR if and only if the vCPU has RTM or HLE

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When emulating CPUID, retrieve MSR_IA32_TSX_CTRL.TSX_CTRL_CPUID_CLEAR if
and only if RTM and/or HLE feature bits need to be cleared.  Getting the
MSR value is unnecessary if neither bit is set, and avoiding the lookup
saves ~80 cycles for vCPUs without RTM or HLE.

Cc: Jim Mattson <jmattson@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20241211013302.1347853-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-12-10 17:33:00 -08:00
parent aa93b6f96f
commit 7e9f735e7a
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kvm/cpuid.c
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@ -1999,7 +1999,8 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
*edx = entry->edx;
if (function == 7 && index == 0) {
u64 data;
if (!__kvm_get_msr(vcpu, MSR_IA32_TSX_CTRL, &data, true) &&
if ((*ebx & (feature_bit(RTM) | feature_bit(HLE))) &&
!__kvm_get_msr(vcpu, MSR_IA32_TSX_CTRL, &data, true) &&
(data & TSX_CTRL_CPUID_CLEAR))
*ebx &= ~(feature_bit(RTM) | feature_bit(HLE));
} else if (function == 0x80000007) {