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Revert "KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible"

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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@google.com

Fixes: 8c9e639da435 ("KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible")
Suggested-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230106011306.85230-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-01-06 01:12:47 +00:00 committed by Paolo Bonzini
parent da3fb46d22
commit f9829c9076
1 changed files with 11 additions and 18 deletions
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29
arch/x86/kvm/svm/avic.c
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@ -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;
}
}