[PATCH 1/7] KVM: x86: document AVIC/APICv inhibit reasons

Maxim Levitsky
2022-06-06T18:08:48Z

These days there are too many AVIC/APICv inhibit
reasons, and it doesn't hurt to have some documentation
for them.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 59 +++++++++++++++++++++++++++++++--
1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6cf5d77d78969..d7fb3ade44501 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1065,14 +1065,69 @@ struct kvm_x86_msr_filter {
};

enum kvm_apicv_inhibit {
+
+ /********************************************************************/
+ /* INHIBITs that are relevant to both Intel's APICv and AMD's AVIC. */
+ /********************************************************************/
+
+ /*
+ * APIC acceleration is disabled by a module parameter
+ * and/or not supported in hardware.
+ */
APICV_INHIBIT_REASON_DISABLE,
+
+ /*
+ * APIC acceleration is inhibited because AutoEOI feature is
+ * being used by a HyperV guest.
+ */
APICV_INHIBIT_REASON_HYPERV,
+
+ /*
+ * APIC acceleration is inhibited because the userspace didn't yet
+ * enable the kernel/split irqchip.
+ */
+ APICV_INHIBIT_REASON_ABSENT,
+
+ /* APIC acceleration is inhibited because KVM_GUESTDBG_BLOCKIRQ
+ * (out of band, debug measure of blocking all interrupts on this vCPU)
+ * was enabled, to avoid AVIC/APICv bypassing it.
+ */
+ APICV_INHIBIT_REASON_BLOCKIRQ,
+
+ /******************************************************/
+ /* INHIBITs that are relevant only to the AMD's AVIC. */
+ /******************************************************/
+
+ /*
+ * AVIC is inhibited on a vCPU because it runs a nested guest.
+ *
+ * This is needed because unlike APICv, the peers of this vCPU
+ * cannot use the doorbell mechanism to signal interrupts via AVIC when
+ * a vCPU runs nested.
+ */
APICV_INHIBIT_REASON_NESTED,
+
+ /*
+ * On SVM, the wait for the IRQ window is implemented with pending vIRQ,
+ * which cannot be injected when the AVIC is enabled, thus AVIC
+ * is inhibited while KVM waits for IRQ window.
+ */
APICV_INHIBIT_REASON_IRQWIN,
+
+ /*
+ * PIT (i8254) 're-inject' mode, relies on EOI intercept,
+ * which AVIC doesn't support for edge triggered interrupts.
+ */
APICV_INHIBIT_REASON_PIT_REINJ,
+
+ /*
+ * AVIC is inhibited because the guest has x2apic in its CPUID.
+ */
APICV_INHIBIT_REASON_X2APIC,
- APICV_INHIBIT_REASON_BLOCKIRQ,
- APICV_INHIBIT_REASON_ABSENT,
+
+ /*
+ * AVIC is disabled because SEV doesn't support it.
+ */
APICV_INHIBIT_REASON_SEV,
};

--
2.26.3