linux-kernel - [RFC PATCH v1 14/37] KVM: selftests: Create gmem fd before "regular" fd when adding memslot

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Message-ID: <5ee20908e7a67204215ed17c502a466a516d0ae6.1760731772.git.ackerleytng@google.com>
Date: Fri, 17 Oct 2025 13:11:55 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: [RFC PATCH v1 14/37] KVM: selftests: Create gmem fd before "regular"
 fd when adding memslot

From: Sean Christopherson <seanjc@...gle.com>

When adding a memslot associated a guest_memfd instance, create/dup the
guest_memfd before creating the "normal" backing file.  This will allow
dup'ing the gmem fd as the normal fd when guest_memfd supports mmap(),
i.e. to make guest_memfd the _only_ backing source for the memslot.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 45 +++++++++++-----------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index eef6de9a7f4b1..e35c65a173606 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1026,6 +1026,29 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	if (alignment > 1)
 		region->mmap_size += alignment;
 
+	if (flags & KVM_MEM_GUEST_MEMFD) {
+		if (guest_memfd < 0) {
+			uint32_t guest_memfd_flags = 0;
+
+			TEST_ASSERT(!guest_memfd_offset,
+				    "Offset must be zero when creating new guest_memfd");
+			guest_memfd = vm_create_guest_memfd(vm, mem_size, guest_memfd_flags);
+		} else {
+			/*
+			 * Install a unique fd for each memslot so that the fd
+			 * can be closed when the region is deleted without
+			 * needing to track if the fd is owned by the framework
+			 * or by the caller.
+			 */
+			guest_memfd = kvm_dup(guest_memfd);
+		}
+
+		region->region.guest_memfd = guest_memfd;
+		region->region.guest_memfd_offset = guest_memfd_offset;
+	} else {
+		region->region.guest_memfd = -1;
+	}
+
 	region->fd = -1;
 	if (backing_src_is_shared(src_type))
 		region->fd = kvm_memfd_alloc(region->mmap_size,
@@ -1055,28 +1078,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 
 	region->backing_src_type = src_type;
 
-	if (flags & KVM_MEM_GUEST_MEMFD) {
-		if (guest_memfd < 0) {
-			uint32_t guest_memfd_flags = 0;
-			TEST_ASSERT(!guest_memfd_offset,
-				    "Offset must be zero when creating new guest_memfd");
-			guest_memfd = vm_create_guest_memfd(vm, mem_size, guest_memfd_flags);
-		} else {
-			/*
-			 * Install a unique fd for each memslot so that the fd
-			 * can be closed when the region is deleted without
-			 * needing to track if the fd is owned by the framework
-			 * or by the caller.
-			 */
-			guest_memfd = kvm_dup(guest_memfd);
-		}
-
-		region->region.guest_memfd = guest_memfd;
-		region->region.guest_memfd_offset = guest_memfd_offset;
-	} else {
-		region->region.guest_memfd = -1;
-	}
-
 	region->unused_phy_pages = sparsebit_alloc();
 	if (vm_arch_has_protected_memory(vm))
 		region->protected_phy_pages = sparsebit_alloc();
-- 
2.51.0.858.gf9c4a03a3a-goog