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KVM: x86: Remove runtime Xen TSC frequency CPUID update

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Remove the code in kvm_cpuid() that dynamically updates the Xen TSC
info CPUID leaf at runtime, as KVM is updating the wrong sub-leaf anyway
(0x40000x03/2 EAX is the *host* TSC frequency per the Xen ABI, not the
guest frequency which belongs in 0x40000x03/0 ECX).

Simply drop the code instead of fixing it to fill the correct sub-leaf, as
modifying guest CPUID entries/output at runtime is generally undesirable,
and providing userspace the necessary data to fill the sub-leaf itself is
useful for other reasons, e.g. to fill the generic 0x40000010 timing leaf
and to provide exact scaling information to aid save/restore.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/20260728144954.355376-23-dwmw2@infradead.org
[sean: tweak changelog to take this patch before the new uAPI]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
David Woodhouse 2026-07-28 15:40:02 +01:00 committed by Sean Christopherson
parent 36a8520064
commit 7d3bd21e45
2 changed files with 0 additions and 29 deletions
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16
arch/x86/kvm/cpuid.c
View File

@ -2117,22 +2117,6 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
} else if (function == 0x80000007) {
if (kvm_hv_invtsc_suppressed(vcpu))
*edx &= ~feature_bit(CONSTANT_TSC);
} else if (IS_ENABLED(CONFIG_KVM_XEN) &&
kvm_xen_is_tsc_leaf(vcpu, function)) {
/*
* Update guest TSC frequency information if necessary.
* Ignore failures, there is no sane value that can be
* provided if KVM can't get the TSC frequency.
*/
if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu))
kvm_guest_time_update(vcpu);
if (index == 1) {
*ecx = vcpu->arch.pvclock_tsc_mul;
*edx = vcpu->arch.pvclock_tsc_shift;
} else if (index == 2) {
*eax = vcpu->arch.hw_tsc_khz;
}
}
} else {
*eax = *ebx = *ecx = *edx = 0;

13
arch/x86/kvm/xen.h
View File

@ -50,14 +50,6 @@ static inline void kvm_xen_sw_enable_lapic(struct kvm_vcpu *vcpu)
kvm_xen_inject_vcpu_vector(vcpu);
}
static inline bool kvm_xen_is_tsc_leaf(struct kvm_vcpu *vcpu, u32 function)
{
return static_branch_unlikely(&kvm_xen_enabled.key) &&
vcpu->arch.xen.cpuid.base &&
function <= vcpu->arch.xen.cpuid.limit &&
function == (vcpu->arch.xen.cpuid.base | XEN_CPUID_LEAF(3));
}
static inline bool kvm_xen_msr_enabled(struct kvm *kvm)
{
return static_branch_unlikely(&kvm_xen_enabled.key) &&
@ -177,11 +169,6 @@ static inline bool kvm_xen_timer_enabled(struct kvm_vcpu *vcpu)
{
return false;
}
static inline bool kvm_xen_is_tsc_leaf(struct kvm_vcpu *vcpu, u32 function)
{
return false;
}
#endif
int kvm_xen_hypercall(struct kvm_vcpu *vcpu);