Re: [PATCH v15 13/23] KVM: selftests: Support guest_memfd in-place conversion

[Binbin Wu]

On 10/2/2026 3:37 AM, Lisa Wang wrote:
> With guest_memfd in-place conversion, the memory region can be set as
> shared, eliminating the need for dual-backed memory.
> 
> By setting the region to shared initially, the KVM selftest framework
> can populate the mmap()-ed guest_memfd memory just like any standard
> memory provider.
> 
> For CoCo VMs, pages that need to be private are explicitly set to
> private before executing the VM.
> 
> Signed-off-by: Lisa Wang <wyihan@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c         | 20 ++++++++++++++------
>  tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c |  6 +++++-
>  2 files changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 7625908caf21..f474664b5d92 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -494,8 +494,10 @@ struct kvm_vm *__vm_create(struct vm_shape shape, u32 nr_runnable_vcpus,
>  	u64 nr_pages = vm_nr_pages_required(shape.mode, nr_runnable_vcpus,
>  						 nr_extra_pages);
>  	struct userspace_mem_region *slot0;
> +	u64 gmem_flags = 0;
>  	struct kvm_vm *vm;
> -	int i, flags;
> +	int flags = 0;
> +	int i;
>  
>  	kvm_set_files_rlimit(nr_runnable_vcpus);
>  
> @@ -505,14 +507,20 @@ struct kvm_vm *__vm_create(struct vm_shape shape, u32 nr_runnable_vcpus,
>  	vm = ____vm_create(shape);
>  
>  	/*
> -	 * Force GUEST_MEMFD for the primary memory region if necessary, e.g.
> -	 * for CoCo VMs that require GUEST_MEMFD backed private memory.
> +	 * Force GUEST_MEMFD for the primary memory region if necessary, and
> +	 * initialize it as shared if in-place conversion is supported, so the
> +	 * selftest framework can populate it exactly like other memory
> +	 * providers.
>  	 */
> -	flags = 0;
> -	if (is_guest_memfd_required(shape))
> +	if (is_guest_memfd_required(shape)) {
>  		flags |= KVM_MEM_GUEST_MEMFD;
> +		if (kvm_has_gmem_attributes)
> +			gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED |
> +				      GUEST_MEMFD_FLAG_MMAP;
> +	}
>  
> -	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, 0, 0, nr_pages, flags);
> +	vm_mem_add(vm, VM_MEM_SRC_ANONYMOUS, 0, 0, nr_pages, flags,
> +		   -1, 0, gmem_flags);

This is common for both TDX and SNP, does it break SNP?


>  	for (i = 0; i < NR_MEM_REGIONS; i++)
>  		vm->memslots[i] = 0;
>  
> diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> index e348507a6be8..40ee9b1951c2 100644
> --- a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> +++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> @@ -23,6 +23,8 @@ void tdx_vm_setup_boot_code_region(struct kvm_vm *vm)
>  	gpa_t gpa;
>  	u8 *hva;
>  
> +	if (kvm_has_gmem_attributes)
> +		gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED | GUEST_MEMFD_FLAG_MMAP;
>  	vm_mem_add(vm, VM_MEM_SRC_SHMEM, alloc_gpa, TD_BOOT_CODE_SLOT,
>  		   nr_pages, KVM_MEM_GUEST_MEMFD, -1, 0, gmem_flags);
>  
> @@ -44,9 +46,11 @@ void tdx_vm_setup_boot_parameters_region(struct kvm_vm *vm, u32 nr_runnable_vcpu
>  	size_t boot_params_size = sizeof(struct td_boot_parameters) +
>  		nr_runnable_vcpus * sizeof(struct td_per_vcpu_parameters);
>  	int npages = DIV_ROUND_UP(boot_params_size, PAGE_SIZE);
> -	const u64 gmem_flags = 0;
> +	u64 gmem_flags = 0;
>  	gpa_t gpa;
>  
> +	if (kvm_has_gmem_attributes)
> +		gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED | GUEST_MEMFD_FLAG_MMAP;
>  	vm_mem_add(vm, VM_MEM_SRC_SHMEM, TD_BOOT_PARAMETERS_GPA,
>  		   TD_BOOT_PARAMETERS_SLOT, npages,
>  		   KVM_MEM_GUEST_MEMFD, -1, 0, gmem_flags);
>