On Fri, 2023-01-06 at 01:13 +0000, Sean Christopherson wrote: > Do not modify AVIC's logical ID table if the logical ID portion of the > LDR is not a power-of-2, i.e. if the LDR has multiple bits set. Taking > only the first bit means that KVM will fail to match MDAs that intersect > with "higher" bits in the "ID" > > The "ID" acts as a bitmap, but is referred to as an ID because there's an > implicit, unenforced "requirement" that software only set one bit. This > edge case is arguably out-of-spec behavior, but KVM cleanly handles it > in all other cases, e.g. the optimized logical map (and AVIC!) is also > disabled in this scenario. > > Refactor the code to consolidate the checks, and so that the code looks > more like avic_kick_target_vcpus_fast(). Very minor nitpick about the subject, it feels like it just changes something minor but it pretty much rewrites the avic_get_logical_id_entry. When I bisected for the bug, this did confuse me a bit. I don't have a good idea on how to call this patch so I won't object to the current subject to stay as well. Best regards, Maxim Levitsky > > Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC") > Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> > Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > arch/x86/kvm/svm/avic.c | 30 +++++++++++++++--------------- > 1 file changed, 15 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c > index 5b33f91b701c..eb979695e7d8 100644 > --- a/arch/x86/kvm/svm/avic.c > +++ b/arch/x86/kvm/svm/avic.c > @@ -513,26 +513,26 @@ unsigned long avic_vcpu_get_apicv_inhibit_reasons(struct kvm_vcpu *vcpu) > static u32 *avic_get_logical_id_entry(struct kvm_vcpu *vcpu, u32 ldr, bool flat) > { > struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm); > - int index; > u32 *logical_apic_id_table; > - int dlid = GET_APIC_LOGICAL_ID(ldr); > + u32 cluster, index; > > - if (!dlid) > - return NULL; > + ldr = GET_APIC_LOGICAL_ID(ldr); > > - if (flat) { /* flat */ > - index = ffs(dlid) - 1; > - if (index > 7) > + if (flat) { > + cluster = 0; > + } else { > + cluster = (ldr >> 4); > + if (cluster >= 0xf) > return NULL; > - } else { /* cluster */ > - int cluster = (dlid & 0xf0) >> 4; > - int apic = ffs(dlid & 0x0f) - 1; > - > - if ((apic < 0) || (apic > 7) || > - (cluster >= 0xf)) > - return NULL; > - index = (cluster << 2) + apic; > + ldr &= 0xf; > } > + if (!ldr || !is_power_of_2(ldr)) > + return NULL; > + > + index = __ffs(ldr); > + if (WARN_ON_ONCE(index > 7)) > + return NULL; > + index += (cluster << 2); > > logical_apic_id_table = (u32 *) page_address(kvm_svm->avic_logical_id_table_page); > Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> Best regards, Maxim Levitsky