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KVM: x86: document AVIC/APICv inhibit reasons

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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>
Message-Id: <20220606180829.102503-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2022-06-06 21:08:23 +03:00 committed by Paolo Bonzini
parent d2263de137
commit a9603ae0e4
1 changed files with 60 additions and 5 deletions
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65
arch/x86/include/asm/kvm_host.h
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@ -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,
APICV_INHIBIT_REASON_NESTED,
APICV_INHIBIT_REASON_IRQWIN,
APICV_INHIBIT_REASON_PIT_REINJ,
APICV_INHIBIT_REASON_X2APIC,
APICV_INHIBIT_REASON_BLOCKIRQ,
/*
* 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,
/*
* AVIC is disabled because SEV doesn't support it.
*/
APICV_INHIBIT_REASON_SEV,
};