KVM: VMX: Use __kvm_faultin_page() to get APIC access page/pfn

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@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-52-seanjc@google.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index bee90089c8a7b08f768bccda984ecbdad759864e..f6900bec4874481c44cb669eb787df22321f9094 100644 (file)
--- 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