linux-kernel - [PATCH v5 07/12] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest

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Message-ID: <20250828093902.2719-8-roypat@amazon.co.uk>
Date: Thu, 28 Aug 2025 09:39:25 +0000
From: "Roy, Patrick" <roypat@...zon.co.uk>
To: "david@...hat.com" <david@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "Roy, Patrick" <roypat@...zon.co.uk>, "tabba@...gle.com"
	<tabba@...gle.com>, "ackerleytng@...gle.com" <ackerleytng@...gle.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "kvmarm@...ts.linux.dev"
	<kvmarm@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"rppt@...nel.org" <rppt@...nel.org>, "will@...nel.org" <will@...nel.org>,
	"vbabka@...e.cz" <vbabka@...e.cz>, "Cali, Marco" <xmarcalx@...zon.co.uk>,
	"Kalyazin, Nikita" <kalyazin@...zon.co.uk>, "Thomson, Jack"
	<jackabt@...zon.co.uk>, "Manwaring, Derek" <derekmn@...zon.com>
Subject: [PATCH v5 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
GUEST_MEMFD_FLAG_MMAP) 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 c3f5142b0a54..cc67dfecbf65 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1107,22 +1107,26 @@ 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;
-- 
2.50.1