On Tue, 29 Jul 2025 at 23:56, Sean Christopherson <seanjc@google.com> wrote:
>
> Add a guest_memfd testcase to verify that a vCPU can fault-in guest_memfd
> memory that supports mmap(), but that is not currently mapped into host
> userspace and/or has a userspace address (in the memslot) that points at
> something other than the target guest_memfd range. Mapping guest_memfd
> memory into the guest is supposed to operate completely independently from
> any userspace mappings.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Cheers,
/fuad
> ---
> .../testing/selftests/kvm/guest_memfd_test.c | 64 +++++++++++++++++++
> 1 file changed, 64 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 088053d5f0f5..b86bf89a71e0 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -13,6 +13,7 @@
>
> #include <linux/bitmap.h>
> #include <linux/falloc.h>
> +#include <linux/sizes.h>
> #include <setjmp.h>
> #include <signal.h>
> #include <sys/mman.h>
> @@ -21,6 +22,7 @@
>
> #include "kvm_util.h"
> #include "test_util.h"
> +#include "ucall_common.h"
>
> static void test_file_read_write(int fd)
> {
> @@ -298,6 +300,66 @@ static void test_guest_memfd(unsigned long vm_type)
> kvm_vm_free(vm);
> }
>
> +static void guest_code(uint8_t *mem, uint64_t size)
> +{
> + size_t i;
> +
> + for (i = 0; i < size; i++)
> + __GUEST_ASSERT(mem[i] == 0xaa,
> + "Guest expected 0xaa at offset %lu, got 0x%x", i, mem[i]);
> +
> + memset(mem, 0xff, size);
> + GUEST_DONE();
> +}
> +
> +static void test_guest_memfd_guest(void)
> +{
> + /*
> + * Skip the first 4gb and slot0. slot0 maps <1gb and is used to back
> + * the guest's code, stack, and page tables, and low memory contains
> + * the PCI hole and other MMIO regions that need to be avoided.
> + */
> + const uint64_t gpa = SZ_4G;
> + const int slot = 1;
> +
> + struct kvm_vcpu *vcpu;
> + struct kvm_vm *vm;
> + uint8_t *mem;
> + size_t size;
> + int fd, i;
> +
> + if (!kvm_has_cap(KVM_CAP_GUEST_MEMFD_MMAP))
> + return;
> +
> + vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code);
> +
> + TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP),
> + "Default VM type should always support guest_memfd mmap()");
> +
> + size = vm->page_size;
> + fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP);
> + vm_set_user_memory_region2(vm, slot, KVM_MEM_GUEST_MEMFD, gpa, size, NULL, fd, 0);
> +
> + mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> + TEST_ASSERT(mem != MAP_FAILED, "mmap() on guest_memfd failed");
> + memset(mem, 0xaa, size);
> + munmap(mem, size);
> +
> + virt_pg_map(vm, gpa, gpa);
> + vcpu_args_set(vcpu, 2, gpa, size);
> + vcpu_run(vcpu);
> +
> + TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
> +
> + mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> + TEST_ASSERT(mem != MAP_FAILED, "mmap() on guest_memfd failed");
> + for (i = 0; i < size; i++)
> + TEST_ASSERT_EQ(mem[i], 0xff);
> +
> + close(fd);
> + kvm_vm_free(vm);
> +}
> +
> int main(int argc, char *argv[])
> {
> unsigned long vm_types, vm_type;
> @@ -314,4 +376,6 @@ int main(int argc, char *argv[])
>
> for_each_set_bit(vm_type, &vm_types, BITS_PER_TYPE(vm_types))
> test_guest_memfd(vm_type);
> +
> + test_guest_memfd_guest();
> }
> --
> 2.50.1.552.g942d659e1b-goog
>