KVM: selftests: Ensure gmem file sizes are multiple of host page size

When creating a guest_memfd file and associated memslot to validate shared
guest memory, size the file+memslot to the maximum of the host or guest
page size.  Attempting to allocate a single guest page will fail if the
host page size is greater than the guest page size, as KVM requires that
the size of memslots and guest_memfd files are a multiple of the host page
size.

For simplicity, verify the entire file can be shared between guest and host,
e.g. instead of trying to validate "partial" mappings.

Fixes: 42188667be38 ("KVM: selftests: Add guest_memfd testcase to fault-in on !mmap()'d memory")
Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
Closes: https://lore.kernel.org/all/0064952b-048c-455d-ad89-e27e5cb82591@linux.dev
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260512155634.772602-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index d6528c6f5e031dd9e93a3b688edc4f30283dae39..253e748c1d4aa8e6701025cd1add7e272c0cfcbc 100644 (file)
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -510,7 +510,12 @@ static void test_guest_memfd_guest(void)
                    "Default VM type should support INIT_SHARED, supported flags = 0x%x",
                    vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS));
 
-       size = vm->page_size;
+       /*
+        * Use the max of the host or guest page size for all operations, as
+        * KVM requires guest_memfd files and memslots to be sized to multiples
+        * of the host page size.
+        */
+       size = max_t(size_t, vm->page_size, page_size);
        fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP |
                                             GUEST_MEMFD_FLAG_INIT_SHARED);
        vm_set_user_memory_region2(vm, slot, KVM_MEM_GUEST_MEMFD, gpa, size, NULL, fd, 0);
@@ -519,7 +524,7 @@ static void test_guest_memfd_guest(void)
        memset(mem, 0xaa, size);
        kvm_munmap(mem, size);
 
-       virt_pg_map(vm, gpa, gpa);
+       virt_map(vm, gpa, gpa, size / vm->page_size);
        vcpu_args_set(vcpu, 2, gpa, size);
        vcpu_run(vcpu);