[PATCH v2 02/12] KVM: arm64: guest_memfd: Check mmap support when preparing memslot

[Steven Price <steven.price@arm.com>]

Check the guest_memfd backing file when deciding whether an arm64
memslot has mappable memory rather than checking whether the slot is
gmem only. A public helper function is added to be able to reuse the
static kvm_gmem_supports_mmap() function.

Signed-off-by: Steven Price <steven.price@arm.com>

---
Changes since v1:
- New patch in v2. Check the guest_memfd backing file rather than the
  memslot flag when deciding whether arm64 can map the backing memory.
---
 arch/arm64/kvm/mmu.c     | 7 ++++---
 include/linux/kvm_host.h | 1 +
 virt/kvm/guest_memfd.c   | 6 ++++++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1db10d8d6db7..a146f6cde3d0 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2839,10 +2839,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		return -EFAULT;
 
 	/*
-	 * Only support guest_memfd backed memslots with mappable memory, since
-	 * there aren't any CoCo VMs that support only private memory on arm64.
+	 * Protected VMs currently require guest_memfd backed memslots with
+	 * mappable memory to support shared mappings.
 	 */
-	if (kvm_slot_has_gmem(new) && !kvm_memslot_is_gmem_only(new))
+	if (kvm_arch_has_private_mem(kvm) && kvm_slot_has_gmem(new) &&
+	    !kvm_gmem_slot_supports_mmap(new))
 		return -EINVAL;
 
 	/* guest_memfd is incompatible with MTE. */
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e7fc94e2910a..f65728a713ec 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2614,6 +2614,7 @@ static inline bool kvm_is_private_gfn(struct kvm *kvm, gfn_t gfn)
 
 #ifdef CONFIG_KVM_GUEST_MEMFD
 bool kvm_gmem_is_private_gfn(struct kvm *kvm, gfn_t gfn);
+bool kvm_gmem_slot_supports_mmap(const struct kvm_memory_slot *slot);
 bool kvm_arch_supports_gmem_init_shared(struct kvm *kvm);
 
 static inline u64 kvm_gmem_get_supported_flags(struct kvm *kvm)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 8c97a69b16dc..3dd8d227bebb 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -442,6 +442,12 @@ static bool kvm_gmem_supports_mmap(struct inode *inode)
 	return GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_MMAP;
 }
 
+bool kvm_gmem_slot_supports_mmap(const struct kvm_memory_slot *slot)
+{
+	/* The guest_memfd file is pinned while preparing a new memslot. */
+	return kvm_gmem_supports_mmap(file_inode(slot->gmem.file));
+}
+
 static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)
 {
 	struct inode *inode = file_inode(vmf->vma->vm_file);
-- 
2.43.0