KVM: guest_memfd: Provide "struct page" as output from kvm_gmem_get_pfn()

Provide the "struct page" associated with a guest_memfd pfn as an output
from __kvm_gmem_get_pfn() so that KVM guest page fault handlers can
directly put the page instead of having to rely on
kvm_pfn_to_refcounted_page().

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: <20241010182427.1434605-47-seanjc@google.com>

4 files changed, 17 insertions, 9 deletions

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2bea2d20c571..c657c3c449c8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4407,7 +4407,7 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
 	}
 
 	r = kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault->pfn,
-			     &max_order);
+			     &fault->refcounted_page, &max_order);
 	if (r) {
 		kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
 		return r;
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 4557ff3804ae..c6c852485900 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3849,6 +3849,7 @@ static int __sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu)
 	if (VALID_PAGE(svm->sev_es.snp_vmsa_gpa)) {
 		gfn_t gfn = gpa_to_gfn(svm->sev_es.snp_vmsa_gpa);
 		struct kvm_memory_slot *slot;
+		struct page *page;
 		kvm_pfn_t pfn;
 
 		slot = gfn_to_memslot(vcpu->kvm, gfn);
@@ -3859,7 +3860,7 @@ static int __sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu)
 		 * The new VMSA will be private memory guest memory, so
 		 * retrieve the PFN from the gmem backend.
 		 */
-		if (kvm_gmem_get_pfn(vcpu->kvm, slot, gfn, &pfn, NULL))
+		if (kvm_gmem_get_pfn(vcpu->kvm, slot, gfn, &pfn, &page, NULL))
 			return -EINVAL;
 
 		/*
@@ -3888,7 +3889,7 @@ static int __sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu)
 		 * changes then care should be taken to ensure
 		 * svm->sev_es.vmsa is pinned through some other means.
 		 */
-		kvm_release_pfn_clean(pfn);
+		kvm_release_page_clean(page);
 	}
 
 	/*
@@ -4688,6 +4689,7 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 	struct kvm_memory_slot *slot;
 	struct kvm *kvm = vcpu->kvm;
 	int order, rmp_level, ret;
+	struct page *page;
 	bool assigned;
 	kvm_pfn_t pfn;
 	gfn_t gfn;
@@ -4714,7 +4716,7 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 		return;
 	}
 
-	ret = kvm_gmem_get_pfn(kvm, slot, gfn, &pfn, &order);
+	ret = kvm_gmem_get_pfn(kvm, slot, gfn, &pfn, &page, &order);
 	if (ret) {
 		pr_warn_ratelimited("SEV: Unexpected RMP fault, no backing page for private GPA 0x%llx\n",
 				    gpa);
@@ -4772,7 +4774,7 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 out:
 	trace_kvm_rmp_fault(vcpu, gpa, pfn, error_code, rmp_level, ret);
 out_no_trace:
-	put_page(pfn_to_page(pfn));
+	kvm_release_page_unused(page);
 }
 
 static bool is_pfn_range_shared(kvm_pfn_t start, kvm_pfn_t end)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a63b0325d3e2..6efdc00b4254 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2487,11 +2487,13 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
 
 #ifdef CONFIG_KVM_PRIVATE_MEM
 int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
-		     gfn_t gfn, kvm_pfn_t *pfn, int *max_order);
+		     gfn_t gfn, kvm_pfn_t *pfn, struct page **page,
+		     int *max_order);
 #else
 static inline int kvm_gmem_get_pfn(struct kvm *kvm,
 				   struct kvm_memory_slot *slot, gfn_t gfn,
-				   kvm_pfn_t *pfn, int *max_order)
+				   kvm_pfn_t *pfn, struct page **page,
+				   int *max_order)
 {
 	KVM_BUG_ON(1, kvm);
 	return -EIO;
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 8a878e57c5d4..47a9f68f7b24 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -594,7 +594,8 @@ static struct folio *__kvm_gmem_get_pfn(struct file *file,
 }
 
 int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
-		     gfn_t gfn, kvm_pfn_t *pfn, int *max_order)
+		     gfn_t gfn, kvm_pfn_t *pfn, struct page **page,
+		     int *max_order)
 {
 	pgoff_t index = kvm_gmem_get_index(slot, gfn);
 	struct file *file = kvm_gmem_get_file(slot);
@@ -615,7 +616,10 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 		r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
 
 	folio_unlock(folio);
-	if (r < 0)
+
+	if (!r)
+		*page = folio_file_page(folio, index);
+	else
 		folio_put(folio);
 
 out: