[PATCH 0/6] RFC: KVM: SVM: Allow L1's AVIC to co-exist with nesting

Maxim Levitsky
2021-12-09T11:55:10Z

This patch series aims to lift long standing restriction of
using AVIC only when nested virtualization is not exposed
to the guest.

Notes about specific patches:

Patch 1 addresses the fact that AVIC appears to be disabled
in CPUID on several Milan systems I am tesing on.
This adds a workaround (with a big warning and a kernel taint) to enable
it anyway if you really know what you are doing.

It is possible that those systems have the AVIC disabled as a workaround
for the AVIC errata #1235 which might be already fixed but OEM might
not yet re-enabled it out of caution.

Patch 6 adds the AVIC co-existance itself, and was tested with a modification
of the ipi_stress unit test which I soon post upstream which made one
of vCPUs enter nested guest and receive the IPI while nested guest is running.

It was tested on a Zen3 (Milan) machine. On Zen2 machines I have errata #1235
makes my test fail quite fast.

Best regards,
Maxim Levitsky

Maxim Levitsky (6):
KVM: SVM: allow to force AVIC to be enabled
KVM: x86: add a tracepoint for APICv/AVIC interrupt delivery
KVM: SVM: fix AVIC race of host->guest IPI delivery vs AVIC inhibition
KVM: SVM: fix races in the AVIC incomplete IPI delivery to vCPUs
KVM: x86: never clear irr_pending in kvm_apic_update_apicv
KVM: SVM: allow AVIC to co-exist with a nested guest running

arch/x86/include/asm/kvm-x86-ops.h | 1 +
arch/x86/include/asm/kvm_host.h | 7 +++++-
arch/x86/kvm/lapic.c | 6 ++++-
arch/x86/kvm/svm/avic.c | 35 +++++++++++++++++++++++-----
arch/x86/kvm/svm/nested.c | 13 ++++++-----
arch/x86/kvm/svm/svm.c | 37 +++++++++++++++++++-----------
arch/x86/kvm/svm/svm.h | 1 +
arch/x86/kvm/trace.h | 24 +++++++++++++++++++
arch/x86/kvm/x86.c | 17 ++++++++++++--
9 files changed, 111 insertions(+), 30 deletions(-)

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2.26.3