On Sat, 2022-10-01 at 00:58 +0000, Sean Christopherson wrote: > Due to a likely mismerge of patches, KVM ended up with a superfluous > commit to "enable" AVIC's fast path for x2AVIC mode. Even worse, the > superfluous commit has several bugs and creates a nasty local shadow > variable. > > Rather than fix the bugs piece-by-piece[*] to achieve the same end > result, revert the patch wholesale. > > Opportunistically add a comment documenting the x2AVIC dependencies. > > This reverts commit 8c9e639da435874fb845c4d296ce55664071ea7a. > > [*] https://lore.kernel.org/all/YxEP7ZBRIuFWhnYJ@xxxxxxxxxx > > Fixes: 8c9e639da435 ("KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible") > Suggested-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > arch/x86/kvm/svm/avic.c | 29 +++++++++++------------------ > 1 file changed, 11 insertions(+), 18 deletions(-) > > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c > index e35e9363e7ff..605c36569ddf 100644 > --- a/arch/x86/kvm/svm/avic.c > +++ b/arch/x86/kvm/svm/avic.c > @@ -378,7 +378,17 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source > > logid_index = cluster + __ffs(bitmap); > > - if (!apic_x2apic_mode(source)) { > + if (apic_x2apic_mode(source)) { > + /* > + * For x2APIC, the logical APIC ID is a read-only value > + * that is derived from the x2APIC ID, thus the x2APIC > + * ID can be found by reversing the calculation (done > + * above). Note, bits 31:20 of the x2APIC ID are not > + * propagated to the logical ID, but KVM limits the > + * x2APIC ID limited to KVM_MAX_VCPU_IDS. > + */ > + l1_physical_id = logid_index; > + } else { > u32 *avic_logical_id_table = > page_address(kvm_svm->avic_logical_id_table_page); > > @@ -393,23 +403,6 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source > > l1_physical_id = logid_entry & > AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK; > - } else { > - /* > - * For x2APIC logical mode, cannot leverage the index. > - * Instead, calculate physical ID from logical ID in ICRH. > - */ > - int cluster = (icrh & 0xffff0000) >> 16; > - int apic = ffs(icrh & 0xffff) - 1; > - > - /* > - * If the x2APIC logical ID sub-field (i.e. icrh[15:0]) > - * contains anything but a single bit, we cannot use the > - * fast path, because it is limited to a single vCPU. > - */ > - if (apic < 0 || icrh != (1 << apic)) > - return -EINVAL; > - > - l1_physical_id = (cluster << 4) + apic; > } > } > Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> Best regards, Maxim Levitsky
