[PATCH v13 13/20] KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory

[Fuad Tabba <tabba@google.com>]

From: Ackerley Tng <ackerleytng@google.com>

Update the KVM MMU fault handler to service guest page faults
for memory slots backed by guest_memfd with mmap support. For such
slots, the MMU must always fault in pages directly from guest_memfd,
bypassing the host's userspace_addr.

This ensures that guest_memfd-backed memory is always handled through
the guest_memfd specific faulting path, regardless of whether it's for
private or non-private (shared) use cases.

Additionally, rename kvm_mmu_faultin_pfn_private() to
kvm_mmu_faultin_pfn_gmem(), as this function is now used to fault in
pages from guest_memfd for both private and non-private memory,
accommodating the new use cases.

Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Co-developed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d997063f76f..cc4cdfea343b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4511,8 +4511,8 @@ static void kvm_mmu_finish_page_fault(struct kvm_vcpu *vcpu,
 				 r == RET_PF_RETRY, fault->map_writable);
 }
 
-static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
-				       struct kvm_page_fault *fault)
+static int kvm_mmu_faultin_pfn_gmem(struct kvm_vcpu *vcpu,
+				    struct kvm_page_fault *fault)
 {
 	int max_order, r;
 
@@ -4537,13 +4537,18 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
 	return RET_PF_CONTINUE;
 }
 
+static bool fault_from_gmem(struct kvm_page_fault *fault)
+{
+	return fault->is_private || kvm_memslot_is_gmem_only(fault->slot);
+}
+
 static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
 				 struct kvm_page_fault *fault)
 {
 	unsigned int foll = fault->write ? FOLL_WRITE : 0;
 
-	if (fault->is_private)
-		return kvm_mmu_faultin_pfn_private(vcpu, fault);
+	if (fault_from_gmem(fault))
+		return kvm_mmu_faultin_pfn_gmem(vcpu, fault);
 
 	foll |= FOLL_NOWAIT;
 	fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll,
-- 
2.50.0.727.gbf7dc18ff4-goog