[PATCH v13 51/85] KVM: VMX: Use __kvm_faultin_page() to get APIC access page/pfn

[Sean Christopherson]

Use __kvm_faultin_page() get the APIC access page so that KVM can
precisely release the refcounted page, i.e. to remove yet another user
of kvm_pfn_to_refcounted_page().  While the path isn't handling a guest
page fault, the semantics are effectively the same; KVM just happens to
be mapping the pfn into a VMCS field instead of a secondary MMU.

Tested-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 851be0820e04..44cc25dfebba 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6790,8 +6790,10 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	struct kvm_memory_slot *slot;
+	struct page *refcounted_page;
 	unsigned long mmu_seq;
 	kvm_pfn_t pfn;
+	bool writable;
 
 	/* Defer reload until vmcs01 is the current VMCS. */
 	if (is_guest_mode(vcpu)) {
@@ -6827,7 +6829,7 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 	 * controls the APIC-access page memslot, and only deletes the memslot
 	 * if APICv is permanently inhibited, i.e. the memslot won't reappear.
 	 */
-	pfn = gfn_to_pfn_memslot(slot, gfn);
+	pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, &writable, &refcounted_page);
 	if (is_error_noslot_pfn(pfn))
 		return;
 
@@ -6838,10 +6840,13 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 		vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));
 
 	/*
-	 * Do not pin apic access page in memory, the MMU notifier
-	 * will call us again if it is migrated or swapped out.
+	 * Do not pin the APIC access page in memory so that it can be freely
+	 * migrated, the MMU notifier will call us again if it is migrated or
+	 * swapped out.  KVM backs the memslot with anonymous memory, the pfn
+	 * should always point at a refcounted page (if the pfn is valid).
 	 */
-	kvm_release_pfn_clean(pfn);
+	if (!WARN_ON_ONCE(!refcounted_page))
+		kvm_release_page_clean(refcounted_page);
 
 	/*
 	 * No need for a manual TLB flush at this point, KVM has already done a
-- 
2.47.0.rc1.288.g06298d1525-goog