[PATCH v2 03/23] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target

Sean Christopherson
2022-09-03T00:23:19Z

Emulate ICR writes on AVIC IPI failures due to invalid targets using the
same logic as failures due to invalid types. AVIC acceleration fails if
_any_ of the targets are invalid, and crucially VM-Exits before sending
IPIs to targets that _are_ valid. In logical mode, the destination is a
bitmap, i.e. a single IPI can target multiple logical IDs. Doing nothing
causes KVM to drop IPIs if at least one target is valid and at least one
target is invalid.

Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/avic.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 4fbef2af1efc..6a3d225eb02c 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -502,14 +502,18 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
trace_kvm_avic_incomplete_ipi(vcpu->vcpu_id, icrh, icrl, id, index);

switch (id) {
+ case AVIC_IPI_FAILURE_INVALID_TARGET:
case AVIC_IPI_FAILURE_INVALID_INT_TYPE:
/*
* Emulate IPIs that are not handled by AVIC hardware, which
- * only virtualizes Fixed, Edge-Triggered INTRs. The exit is
- * a trap, e.g. ICR holds the correct value and RIP has been
- * advanced, KVM is responsible only for emulating the IPI.
- * Sadly, hardware may sometimes leave the BUSY flag set, in
- * which case KVM needs to emulate the ICR write as well in
+ * only virtualizes Fixed, Edge-Triggered INTRs, and falls over
+ * if _any_ targets are invalid, e.g. if the logical mode mask
+ * is a superset of running vCPUs.
+ *
+ * The exit is a trap, e.g. ICR holds the correct value and RIP
+ * has been advanced, KVM is responsible only for emulating the
+ * IPI. Sadly, hardware may sometimes leave the BUSY flag set,
+ * in which case KVM needs to emulate the ICR write as well in
* order to clear the BUSY flag.
*/
if (icrl & APIC_ICR_BUSY)
@@ -525,8 +529,6 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
*/
avic_kick_target_vcpus(vcpu->kvm, apic, icrl, icrh, index);
break;
- case AVIC_IPI_FAILURE_INVALID_TARGET:
- break;
case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
WARN_ONCE(1, "Invalid backing page\n");
break;
--
2.37.2.789.g6183377224-goog