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KVM: x86: Return the VM's configured APIC bus frequency when queried

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When KVM_CAP_X86_APIC_BUS_CYCLES_NS is queried on a specific VM, return the
VM's configured APIC bus frequency, not KVM's default.  Aside from the fact
that returning the default frequency is blatantly wrong if userspace has
changed the frequency, returning the configured frequency means userspace
can blindly trust the result, e.g. when filling PV CPUID information that
communicates the APIC bus frequency to the guest.

Fixes: 6fef518594 ("KVM: x86: Add a capability to configure bus frequency for APIC timer")
Reported-by: David Woodhouse <dwmw2@infradead.org>
Closes: https://lore.kernel.org/all/ab84153e33fbe7c25667f595c56b310d4d5a93ef.camel@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260522173526.3539407-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2026-05-22 10:35:25 -07:00 committed by Paolo Bonzini
parent 2d42c7cf1a
commit 86e2de10eb
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/x86.c
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@ -4876,7 +4876,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = tdp_enabled;
break;
case KVM_CAP_X86_APIC_BUS_CYCLES_NS:
r = APIC_BUS_CYCLE_NS_DEFAULT;
r = kvm ? kvm->arch.apic_bus_cycle_ns : APIC_BUS_CYCLE_NS_DEFAULT;
break;
case KVM_CAP_EXIT_HYPERCALL:
r = KVM_EXIT_HYPERCALL_VALID_MASK;