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Subject[PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts
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From: Oliver Upton <oupton@google.com>

vmx_guest_apic_has_interrupts implicitly depends on the virtual APIC
page being present + mapped into the kernel address space. However, with
demand paging we break this dependency, as the KVM_REQ_GET_VMCS12_PAGES
event isn't assessed before entering vcpu_block.

Fix this by getting vmcs12 pages before inspecting the guest's APIC
page. Note that upstream does not have this issue, as they will directly
get the vmcs12 pages on vmlaunch/vmresume instead of relying on the
event request mechanism. However, the upstream approach is problematic,
as the vmcs12 pages will not be present if a live migration occurred
before checking the virtual APIC page.

Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
arch/x86/kvm/x86.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5366f884e9a7..1d3d8127aaea 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10599,6 +10599,23 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
{
bool hv_timer;

+ /*
+ * We must first get the vmcs12 pages before checking for interrupts
+ * that might unblock the guest if L1 is using virtual-interrupt
+ * delivery.
+ */
+ if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
+ /*
+ * If we have to ask user-space to post-copy a page,
+ * then we have to keep trying to get all of the
+ * VMCS12 pages until we succeed.
+ */
+ if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
+ kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
+ return 0;
+ }
+ }
+
if (!kvm_arch_vcpu_runnable(vcpu)) {
/*
* Switch to the software timer before halt-polling/blocking as
--
2.37.1.455.g008518b4e5-goog
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