linux-kernel - [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts

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Message-Id: <20220802230718.1891356-2-mizhang@google.com>
Date:   Tue,  2 Aug 2022 23:07:14 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Upton <oupton@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts

From: Oliver Upton <oupton@...gle.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@...gle.com>
Signed-off-by: Mingwei Zhang <mizhang@...gle.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