| Message ID | 20210424004645.3950558-15-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: vCPU RESET/INIT fixes and consolidation | expand |
On Fri, Apr 23, 2021 at 5:50 PM Sean Christopherson <seanjc@google.com> wrote: > > Don't set the BSP bit in vcpu->arch.apic_base when the local APIC is > managed by userspace. Forcing all vCPUs to be BSPs is non-sensical, and > was dead code when it was added by commit 97222cc83163 ("KVM: Emulate > local APIC in kernel"). At the time, kvm_lapic_set_base() was invoked > if and only if the local APIC was in-kernel (and it couldn't be called > before the vCPU created its APIC). > > kvm_lapic_set_base() eventually gained generic usage, but the latent bug > escaped notice because the only true consumer would be the guest itself > in the form of an explicit RDMSRs on APs. Out of Linux, SeaBIOS, and > EDK2/OVMF, only OVMF consume the BSP bit from the APIC_BASE MSR. For > the vast majority of usage in OVMF, BSP confusion would be benign. > OVMF's BSP election upon SMI rendezvous might be broken, but practically > no one runs KVM with an out-of-kernel local APIC, let alone does so while > utilizing SMIs with OVMF. > > Fixes: 97222cc83163 ("KVM: Emulate local APIC in kernel") > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Reiji Watanabe <reijiw@google.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index b99630c6d7fe..c11f23753a5b 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2252,9 +2252,6 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value) u64 old_value = vcpu->arch.apic_base; struct kvm_lapic *apic = vcpu->arch.apic; - if (!apic) - value |= MSR_IA32_APICBASE_BSP; - vcpu->arch.apic_base = value; if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE)
Don't set the BSP bit in vcpu->arch.apic_base when the local APIC is managed by userspace. Forcing all vCPUs to be BSPs is non-sensical, and was dead code when it was added by commit 97222cc83163 ("KVM: Emulate local APIC in kernel"). At the time, kvm_lapic_set_base() was invoked if and only if the local APIC was in-kernel (and it couldn't be called before the vCPU created its APIC). kvm_lapic_set_base() eventually gained generic usage, but the latent bug escaped notice because the only true consumer would be the guest itself in the form of an explicit RDMSRs on APs. Out of Linux, SeaBIOS, and EDK2/OVMF, only OVMF consume the BSP bit from the APIC_BASE MSR. For the vast majority of usage in OVMF, BSP confusion would be benign. OVMF's BSP election upon SMI rendezvous might be broken, but practically no one runs KVM with an out-of-kernel local APIC, let alone does so while utilizing SMIs with OVMF. Fixes: 97222cc83163 ("KVM: Emulate local APIC in kernel") Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/lapic.c | 3 --- 1 file changed, 3 deletions(-)