[PATCH v2 1/4] KVM: x86: move the event handling of KVM_REQ_GET_VMCS12_PAGES into a common function

[Mingwei Zhang]

Create a common function to handle kvm request in the vcpu_run loop. KVM
implicitly assumes the virtual APIC page being present + mapped into the
kernel address space when executing vmx_guest_apic_has_interrupts().
However, with demand paging KVM breaks the assumption, 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.
Because of this fix, the event handling code of
KVM_REQ_GET_NESTED_STATE_PAGES becomes a common code path for both
vcpu_enter_guest() and vcpu_block(). Thus, put this code snippet into a
common helper function to avoid code duplication.

Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Originally-by: Oliver Upton <oupton@xxxxxxxxxx>
Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d7374d768296..3dcaac8f0584 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10261,12 +10261,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			r = -EIO;
 			goto out;
 		}
-		if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
-			if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
-				r = 0;
-				goto out;
-			}
-		}
 		if (kvm_check_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu))
 			kvm_mmu_free_obsolete_roots(vcpu);
 		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
@@ -10666,6 +10660,23 @@ static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
 		!vcpu->arch.apf.halted);
 }
 
+static int kvm_vcpu_handle_common_requests(struct kvm_vcpu *vcpu)
+{
+	if (kvm_request_pending(vcpu)) {
+		/*
+		 * 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 (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu)))
+				return 0;
+		}
+	}
+
+	return 1;
+}
+
 /* Called within kvm->srcu read side.  */
 static int vcpu_run(struct kvm_vcpu *vcpu)
 {
@@ -10681,6 +10692,12 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 		 * this point can start executing an instruction.
 		 */
 		vcpu->arch.at_instruction_boundary = false;
+
+		/* Process common request regardless of vcpu state. */
+		r = kvm_vcpu_handle_common_requests(vcpu);
+		if (r <= 0)
+			break;
+
 		if (kvm_vcpu_running(vcpu)) {
 			r = vcpu_enter_guest(vcpu);
 		} else {
-- 
2.37.2.672.g94769d06f0-goog