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Message-ID: <4a1ad1015657e90db1e81c1b51dc07f62afe29ea.1760731772.git.ackerleytng@google.com>
Date: Fri, 17 Oct 2025 13:12:15 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: cgroups@...r.kernel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: [RFC PATCH v1 34/37] KVM: selftests: Update private_mem_conversions_test
to mmap() guest_memfd
Update the private memory conversions selftest to also test conversions
that are done "in-place" via per-guest_memfd memory attributes. In-place
conversions require the host to be able to mmap() the guest_memfd so that
the host and guest can share the same backing physical memory.
This includes several updates, that are conditioned on the system
supporting per-guest_memfd attributes (kvm_has_gmem_attributes):
1. Set up guest_memfd requesting MMAP and INIT_SHARED.
2. With in-place conversions, the host's mapping points directly to the
guest's memory. When the guest converts a region to private, host access
to that region is blocked. Update the test to expect a SIGBUS when
attempting to access the host virtual address (HVA) of private memory.
3. Use vm_mem_set_memory_attributes(), which chooses how to set memory
attributes based on whether kvm_has_gmem_attributes.
Restrict the test to using VM_MEM_SRC_SHMEM because guest_memfd's required
mmap() flags and page sizes happens to align with those of
VM_MEM_SRC_SHMEM. As long as VM_MEM_SRC_SHMEM is used for src_type,
vm_mem_add() works as intended.
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Co-developed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
.../kvm/x86/private_mem_conversions_test.c | 44 ++++++++++++++++---
1 file changed, 37 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
index 814187d06fcca..6730923af830c 100644
--- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
+++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
@@ -309,8 +309,8 @@ static void handle_exit_hypercall(struct kvm_vcpu *vcpu)
vm_guest_mem_fallocate(vm, gpa, size, map_shared);
if (set_attributes)
- vm_set_memory_attributes(vm, gpa, size,
- map_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE);
+ vm_mem_set_memory_attributes(vm, gpa, size,
+ map_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE);
run->hypercall.ret = 0;
}
@@ -354,8 +354,20 @@ static void *__test_mem_conversions(void *__vcpu)
size_t nr_bytes = min_t(size_t, vm->page_size, size - i);
uint8_t *hva = addr_gpa2hva(vm, gpa + i);
- /* In all cases, the host should observe the shared data. */
- memcmp_h(hva, gpa + i, uc.args[3], nr_bytes);
+ /*
+ * When using per-guest_memfd memory attributes,
+ * i.e. in-place conversion, host accesses will
+ * point at guest memory and should SIGBUS when
+ * guest memory is private. When using per-VM
+ * attributes, i.e. separate backing for shared
+ * vs. private, the host should always observe
+ * the shared data.
+ */
+ if (kvm_has_gmem_attributes &&
+ uc.args[0] == SYNC_PRIVATE)
+ TEST_EXPECT_SIGBUS(READ_ONCE(*hva));
+ else
+ memcmp_h(hva, gpa + i, uc.args[3], nr_bytes);
/* For shared, write the new pattern to guest memory. */
if (uc.args[0] == SYNC_SHARED)
@@ -384,6 +396,7 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
const size_t slot_size = memfd_size / nr_memslots;
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
pthread_t threads[KVM_MAX_VCPUS];
+ uint64_t gmem_flags;
struct kvm_vm *vm;
int memfd, i;
@@ -399,12 +412,17 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
vm_enable_cap(vm, KVM_CAP_EXIT_HYPERCALL, (1 << KVM_HC_MAP_GPA_RANGE));
- memfd = vm_create_guest_memfd(vm, memfd_size, 0);
+ if (kvm_has_gmem_attributes)
+ gmem_flags = GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_INIT_SHARED;
+ else
+ gmem_flags = 0;
+
+ memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);
for (i = 0; i < nr_memslots; i++)
vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i,
BASE_DATA_SLOT + i, slot_size / vm->page_size,
- KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, 0);
+ KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, gmem_flags);
for (i = 0; i < nr_vcpus; i++) {
uint64_t gpa = BASE_DATA_GPA + i * per_cpu_size;
@@ -454,17 +472,29 @@ static void usage(const char *cmd)
int main(int argc, char *argv[])
{
- enum vm_mem_backing_src_type src_type = DEFAULT_VM_MEM_SRC;
+ enum vm_mem_backing_src_type src_type;
uint32_t nr_memslots = 1;
uint32_t nr_vcpus = 1;
int opt;
TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));
+ src_type = kvm_has_gmem_attributes ? VM_MEM_SRC_SHMEM :
+ DEFAULT_VM_MEM_SRC;
+
while ((opt = getopt(argc, argv, "hm:s:n:")) != -1) {
switch (opt) {
case 's':
src_type = parse_backing_src_type(optarg);
+ if (kvm_has_gmem_attributes && src_type != VM_MEM_SRC_SHMEM) {
+ printf("Overriding mem_type to %s to test in-place conversions\n",
+ vm_mem_backing_src_alias(VM_MEM_SRC_SHMEM)->name);
+ /*
+ * Use VM_MEM_SRC_SHMEM, whose size and mmap flags
+ * align with those of guest_memfd.
+ */
+ src_type = VM_MEM_SRC_SHMEM;
+ }
break;
case 'n':
nr_vcpus = atoi_positive("nr_vcpus", optarg);
--
2.51.0.858.gf9c4a03a3a-goog
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