Commit a9603ae0 authored by Maxim Levitsky's avatar Maxim Levitsky Committed by Paolo Bonzini
Browse files

KVM: x86: document AVIC/APICv inhibit reasons 



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

Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220606180829.102503-2-mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent d2263de1

arch/x86/include/asm/kvm_host.h

+57 −2
Original line number Diff line number Diff line
@@ -1047,14 +1047,69 @@ 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,

};