Commit 86e2de10 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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



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: 6fef5185 ("KVM: x86: Add a capability to configure bus frequency for APIC timer")
Reported-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
Closes: https://lore.kernel.org/all/ab84153e33fbe7c25667f595c56b310d4d5a93ef.camel@infradead.org


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-ID: <20260522173526.3539407-2-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 2d42c7cf

arch/x86/kvm/x86.c

+1 −1
Original line number Diff line number Diff line
@@ -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;