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

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

[Sean Christopherson]

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>
---
 tools/testing/selftests/kvm/guest_memfd_test.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index d6528c6f5e03..253e748c1d4a 100644
--- 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);
 

base-commit: 6d35786de28116ecf78797a62b84e6bf3c45aa5a
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH] KVM: selftests: Ensure gmem file sizes are multiple of host page size

[Paolo Bonzini]

On 5/12/26 17:56, Sean Christopherson wrote:
> 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>

Queued, thanks.

Paolo

> ---
>   tools/testing/selftests/kvm/guest_memfd_test.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index d6528c6f5e03..253e748c1d4a 100644
> --- 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);
>   
> 
> base-commit: 6d35786de28116ecf78797a62b84e6bf3c45aa5a