linux-kernel - [PATCH v4 07/12] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest

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Message-ID: <20250221160728.1584559-8-roypat@amazon.co.uk>
Date: Fri, 21 Feb 2025 16:07:20 +0000
From: Patrick Roy <roypat@...zon.co.uk>
To: <rppt@...nel.org>, <david@...hat.com>, <seanjc@...gle.com>
CC: Patrick Roy <roypat@...zon.co.uk>, <pbonzini@...hat.com>,
	<corbet@....net>, <willy@...radead.org>, <akpm@...ux-foundation.org>,
	<song@...nel.org>, <jolsa@...nel.org>, <ast@...nel.org>,
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	<jannh@...gle.com>, <shuah@...nel.org>, <kvm@...r.kernel.org>,
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	<linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>, <bpf@...r.kernel.org>,
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Subject: [PATCH v4 07/12] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd != -1

Have vm_mem_add() always set KVM_MEM_GUEST_MEMFD in the memslot flags if
a guest_memfd is passed in as an argument. This eliminates the
possibility where a guest_memfd instance is passed to vm_mem_add(), but
it ends up being ignored because the flags argument does not specify
KVM_MEM_GUEST_MEMFD at the same time.

This makes it easy to support more scenarios in which no vm_mem_add() is
not passed a guest_memfd instance, but is expected to allocate one.
Currently, this only happens if guest_memfd == -1 but flags &
KVM_MEM_GUEST_MEMFD != 0, but later vm_mem_add() will gain support for
loading the test code itself into guest_memfd (via KVM_GMEM_SHARED_MEM)
if requested via a special vm_mem_backing_src_type, at which point
having to make sure the src_type and flags are in-sync becomes
cumbersome.

Signed-off-by: Patrick Roy <roypat@...zon.co.uk>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 26 +++++++++++++---------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 33fefeb3ca44..ebdf38e2983b 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1017,22 +1017,26 @@ 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) {
+	if (guest_memfd < 0) {
+		if (flags & KVM_MEM_GUEST_MEMFD) {
 			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 = dup(guest_memfd);
-			TEST_ASSERT(guest_memfd >= 0, __KVM_SYSCALL_ERROR("dup()", guest_memfd));
 		}
+	} 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 = dup(guest_memfd);
+		TEST_ASSERT(guest_memfd >= 0, __KVM_SYSCALL_ERROR("dup()", guest_memfd));
+	}
+
+	if (guest_memfd > 0) {
+		flags |= KVM_MEM_GUEST_MEMFD;
 
 		region->region.guest_memfd = guest_memfd;
 		region->region.guest_memfd_offset = guest_memfd_offset;
-- 
2.48.1