KVM: nVMX: Use kvm_vcpu_map() to get/pin vmcs12's APIC-access page

Use kvm_vcpu_map() to get/pin the backing for vmcs12's APIC-access page,
there's no reason it has to be restricted to 'struct page' backing.  The
APIC-access page actually doesn't need to be backed by anything, which is
ironically why it got left behind by the series which introduced
kvm_vcpu_map()[1]; the plan was to shove a dummy pfn into vmcs02[2], but
that code never got merged.

Switching the APIC-access page to kvm_vcpu_map() doesn't preclude using a
magic pfn in the future, and will allow a future patch to drop
kvm_vcpu_gpa_to_page().

[1] https://lore.kernel.org/all/1547026933-31226-1-git-send-email-karahmed@amazon.de
[2] https://lore.kernel.org/lkml/1543845551-4403-1-git-send-email-karahmed@amazon.deSigned-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220429010416.2788472-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -311,11 +311,12 @@ static void free_nested(struct kvm_vcpu *vcpu)
 	vmx->nested.cached_vmcs12 = NULL;
 	kfree(vmx->nested.cached_shadow_vmcs12);
 	vmx->nested.cached_shadow_vmcs12 = NULL;
-	/* Unpin physical memory we referred to in the vmcs02 */
-	if (vmx->nested.apic_access_page) {
-		kvm_release_page_clean(vmx->nested.apic_access_page);
-		vmx->nested.apic_access_page = NULL;
-	}
+	/*
+	 * Unpin physical memory we referred to in the vmcs02.  The APIC access
+	 * page's backing page (yeah, confusing) shouldn't actually be accessed,
+	 * and if it is written, the contents are irrelevant.
+	 */
+	kvm_vcpu_unmap(vcpu, &vmx->nested.apic_access_page_map, false);
 	kvm_vcpu_unmap(vcpu, &vmx->nested.virtual_apic_map, true);
 	kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map, true);
 	vmx->nested.pi_desc = NULL;
@@ -3164,8 +3165,6 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct kvm_host_map *map;
-	struct page *page;
-	u64 hpa;
 
 	if (!vcpu->arch.pdptrs_from_userspace &&
 	    !nested_cpu_has_ept(vmcs12) && is_pae_paging(vcpu)) {
@@ -3180,23 +3179,12 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 
 
 	if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
-		/*
-		 * Translate L1 physical address to host physical
-		 * address for vmcs02. Keep the page pinned, so this
-		 * physical address remains valid. We keep a reference
-		 * to it so we can release it later.
-		 */
-		if (vmx->nested.apic_access_page) { /* shouldn't happen */
-			kvm_release_page_clean(vmx->nested.apic_access_page);
-			vmx->nested.apic_access_page = NULL;
-		}
-		page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->apic_access_addr);
-		if (!is_error_page(page)) {
-			vmx->nested.apic_access_page = page;
-			hpa = page_to_phys(vmx->nested.apic_access_page);
-			vmcs_write64(APIC_ACCESS_ADDR, hpa);
+		map = &vmx->nested.apic_access_page_map;
+
+		if (!kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->apic_access_addr), map)) {
+			vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(map->pfn));
 		} else {
-			pr_debug_ratelimited("%s: no backing 'struct page' for APIC-access address in vmcs12\n",
+			pr_debug_ratelimited("%s: no backing for APIC-access address in vmcs12\n",
 					     __func__);
 			vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 			vcpu->run->internal.suberror =
@@ -4632,10 +4620,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
 	}
 
 	/* Unpin physical memory we referred to in vmcs02 */
-	if (vmx->nested.apic_access_page) {
-		kvm_release_page_clean(vmx->nested.apic_access_page);
-		vmx->nested.apic_access_page = NULL;
-	}
+	kvm_vcpu_unmap(vcpu, &vmx->nested.apic_access_page_map, false);
 	kvm_vcpu_unmap(vcpu, &vmx->nested.virtual_apic_map, true);
 	kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map, true);
 	vmx->nested.pi_desc = NULL;

arch/x86/kvm/vmx/vmx.h

@@ -204,7 +204,7 @@ struct nested_vmx {
 	 * Guest pages referred to in the vmcs02 with host-physical
 	 * pointers, so we must keep them pinned while L2 runs.
 	 */
-	struct page *apic_access_page;
+	struct kvm_host_map apic_access_page_map;
 	struct kvm_host_map virtual_apic_map;
 	struct kvm_host_map pi_desc_map;