KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory

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>
[sean: drop the helper]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20250729225455.670324-17-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e83d666f32ad52ed06bf62c6d7ee1f9f8f6ad5e2..56c80588efa0cac5132a990ce658dfc9a3c2e8a1 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4561,8 +4561,8 @@ 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;
 
@@ -4589,8 +4589,8 @@ static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
 {
        unsigned int foll = fault->write ? FOLL_WRITE : 0;
 
-       if (fault->is_private)
-               return kvm_mmu_faultin_pfn_private(vcpu, fault);
+       if (fault->is_private || kvm_memslot_is_gmem_only(fault->slot))
+               return kvm_mmu_faultin_pfn_gmem(vcpu, fault);
 
        foll |= FOLL_NOWAIT;
        fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll,