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KVM: nSVM: Raise event on nested VM exit if L1 doesn't intercept IRQs

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If L1 doesn't intercept interrupts, then KVM will use vmcb02's V_IRQ
to detect an interrupt window for L1 IRQs.  On a subsequent nested
VM-Exit, KVM might need to copy the current V_IRQ from vmcb02 to vmcb01
to continue waiting for an interrupt window, i.e. if there is still a
pending IRQ for L1.

Raise KVM_REQ_EVENT on nested exit if L1 isn't intercepting IRQs to ensure
that KVM will re-enable interrupt window detection if needed.

Note that this is a theoretical bug because KVM already raises
KVM_REQ_EVENT on each nested VM exit, because the nested VM exit resets
RFLAGS and kvm_set_rflags() raises the KVM_REQ_EVENT unconditionally.

Explicitly raise KVM_REQ_EVENT for the interrupt window case to avoid
having an unnecessary dependency on kvm_set_rflags(), and to document
the scenario.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
[santosh: reworded description as per Sean's v2 comment]
Signed-off-by: Santosh Shukla <Santosh.Shukla@amd.com>
Link: https://lore.kernel.org/r/20230227084016.3368-4-santosh.shukla@amd.com
[sean: further massage changelog and comment]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Maxim Levitsky 2023-02-27 14:10:08 +05:30 committed by Sean Christopherson
parent 7334ede457
commit 5d1ec45652
1 changed files with 22 additions and 0 deletions
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22
arch/x86/kvm/svm/nested.c
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@ -1025,6 +1025,28 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
svm_switch_vmcb(svm, &svm->vmcb01);
/*
* Rules for synchronizing int_ctl bits from vmcb02 to vmcb01:
*
* V_IRQ, V_IRQ_VECTOR, V_INTR_PRIO_MASK, V_IGN_TPR: If L1 doesn't
* intercept interrupts, then KVM will use vmcb02's V_IRQ (and related
* flags) to detect interrupt windows for L1 IRQs (even if L1 uses
* virtual interrupt masking). Raise KVM_REQ_EVENT to ensure that
* KVM re-requests an interrupt window if necessary, which implicitly
* copies this bits from vmcb02 to vmcb01.
*
* V_TPR: If L1 doesn't use virtual interrupt masking, then L1's vTPR
* is stored in vmcb02, but its value doesn't need to be copied from/to
* vmcb01 because it is copied from/to the virtual APIC's TPR register
* on each VM entry/exit.
*
* V_GIF: If nested vGIF is not used, KVM uses vmcb02's V_GIF for L1's
* V_GIF. However, GIF is architecturally clear on each VM exit, thus
* there is no need to copy V_GIF from vmcb02 to vmcb01.
*/
if (!nested_exit_on_intr(svm))
kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
svm_copy_lbrs(vmcb12, vmcb02);
svm_update_lbrv(vcpu);