linux-kernel - Re: [PATCH 4/6] KVM: selftests: Add test coverage for guest_memfd without GUEST_MEMFD_FLAG

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Message-ID: <00838b58-06ba-4468-a226-8e20bf1fd773@redhat.com>
Date: Mon, 29 Sep 2025 11:21:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Fuad Tabba <tabba@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>
Subject: Re: [PATCH 4/6] KVM: selftests: Add test coverage for guest_memfd
 without GUEST_MEMFD_FLAG_MMAP

On 26.09.25 18:31, Sean Christopherson wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
> 
> If a VM type supports KVM_CAP_GUEST_MEMFD_MMAP, the guest_memfd test will
> run all test cases with GUEST_MEMFD_FLAG_MMAP set.  This leaves the code
> path for creating a non-mmap()-able guest_memfd on a VM that supports
> mappable guest memfds untested.
> 
> Refactor the test to run the main test suite with a given set of flags.
> Then, for VM types that support the mappable capability, invoke the test
> suite twice: once with no flags, and once with GUEST_MEMFD_FLAG_MMAP
> set.
> 
> This ensures both creation paths are properly exercised on capable VMs.
> 
> test_guest_memfd_flags() tests valid flags, hence it can be run just once
> per VM type, and valid flag identification can be moved into the test
> function.
> 
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> [sean: use double-underscores for the inner helper]
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   .../testing/selftests/kvm/guest_memfd_test.c  | 30 ++++++++++++-------
>   1 file changed, 19 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 60c6dec63490..5a50a28ce1fa 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -239,11 +239,16 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
>   	close(fd1);
>   }
>   
> -static void test_guest_memfd_flags(struct kvm_vm *vm, uint64_t valid_flags)
> +static void test_guest_memfd_flags(struct kvm_vm *vm)
>   {
> +	uint64_t valid_flags = 0;
>   	uint64_t flag;
>   	int fd;
>   
> +	if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
> +		valid_flags |= GUEST_MEMFD_FLAG_MMAP |
> +			       GUEST_MEMFD_FLAG_DEFAULT_SHARED;
> +
>   	for (flag = BIT(0); flag; flag <<= 1) {
>   		fd = __vm_create_guest_memfd(vm, page_size, flag);
>   		if (flag & valid_flags) {
> @@ -267,16 +272,8 @@ do {									\
>   	close(fd);							\
>   } while (0)
>   
> -static void test_guest_memfd(unsigned long vm_type)
> +static void __test_guest_memfd(struct kvm_vm *vm, uint64_t flags)
>   {
> -	uint64_t flags = 0;
> -	struct kvm_vm *vm;
> -
> -	vm = vm_create_barebones_type(vm_type);
> -
> -	if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
> -		flags |= GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_DEFAULT_SHARED;
> -
>   	test_create_guest_memfd_multiple(vm);
>   	test_create_guest_memfd_invalid_sizes(vm, flags);
>   
> @@ -292,8 +289,19 @@ static void test_guest_memfd(unsigned long vm_type)
>   	gmem_test(file_size, vm, flags);
>   	gmem_test(fallocate, vm, flags);
>   	gmem_test(invalid_punch_hole, vm, flags);
> +}
>   
> -	test_guest_memfd_flags(vm, flags);
> +static void test_guest_memfd(unsigned long vm_type)
> +{
> +	struct kvm_vm *vm = vm_create_barebones_type(vm_type);
> +
> +	test_guest_memfd_flags(vm);
> +
> +	__test_guest_memfd(vm, 0);

Having a simple test_guest_memfd_noflags() wrapper might make this 
easier to read.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb