linux-kernel - Re: [PATCH v8 08/30] KVM: selftests: TDX: Update load_td_memory_region() for VM memory backed by guest memfd

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Message-ID: <6899fbff3458b_1d882b29492@iweiny-mobl.notmuch>
Date: Mon, 11 Aug 2025 09:19:43 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Sagi Shahar <sagis@...gle.com>, <linux-kselftest@...r.kernel.org>, "Paolo
 Bonzini" <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, "Sean
 Christopherson" <seanjc@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>,
	Ryan Afranji <afranji@...gle.com>, Andrew Jones <ajones@...tanamicro.com>,
	Isaku Yamahata <isaku.yamahata@...el.com>, Erdem Aktas
	<erdemaktas@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, "Roger
 Wang" <runanwang@...gle.com>, Binbin Wu <binbin.wu@...ux.intel.com>, "Oliver
 Upton" <oliver.upton@...ux.dev>, "Pratik R. Sampat"
	<pratikrajesh.sampat@....com>, Reinette Chatre <reinette.chatre@...el.com>,
	Ira Weiny <ira.weiny@...el.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v8 08/30] KVM: selftests: TDX: Update
 load_td_memory_region() for VM memory backed by guest memfd

Sagi Shahar wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
> 
> If guest memory is backed by restricted memfd
                                          ^^^^^^
                                          guest_memfd?

I'm not sure what a restricted memfd is?

> + UPM is being used, hence encrypted memory region has to be

What is UPM?

Ira

>   registered
> + Can avoid making a copy of guest memory before getting TDX to
>   initialize the memory region
> 
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> Signed-off-by: Sagi Shahar <sagis@...gle.com>
> ---
>  .../selftests/kvm/lib/x86/tdx/tdx_util.c      | 38 +++++++++++++++----
>  1 file changed, 30 insertions(+), 8 deletions(-)
> 
> 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 bb074af4a476..e2bf9766dc03 100644
> --- a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> +++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> @@ -324,6 +324,21 @@ static void tdx_td_finalize_mr(struct kvm_vm *vm)
>  	tdx_ioctl(vm->fd, KVM_TDX_FINALIZE_VM, 0, NULL);
>  }
>  
> +/*
> + * Other ioctls
> + */
> +
> +/*
> + * Register a memory region that may contain encrypted data in KVM.
> + */
> +static void register_encrypted_memory_region(struct kvm_vm *vm,
> +					     struct userspace_mem_region *region)
> +{
> +	vm_set_memory_attributes(vm, region->region.guest_phys_addr,
> +				 region->region.memory_size,
> +				 KVM_MEMORY_ATTRIBUTE_PRIVATE);
> +}
> +
>  /*
>   * TD creation/setup/finalization
>   */
> @@ -459,28 +474,35 @@ static void load_td_memory_region(struct kvm_vm *vm,
>  	if (!sparsebit_any_set(pages))
>  		return;
>  
> +	if (region->region.guest_memfd != -1)
> +		register_encrypted_memory_region(vm, region);
> +
>  	sparsebit_for_each_set_range(pages, i, j) {
>  		const uint64_t size_to_load = (j - i + 1) * vm->page_size;
>  		const uint64_t offset =
>  			(i - lowest_page_in_region) * vm->page_size;
>  		const uint64_t hva = hva_base + offset;
>  		const uint64_t gpa = gpa_base + offset;
> -		void *source_addr;
> +		void *source_addr = (void *)hva;
>  
>  		/*
>  		 * KVM_TDX_INIT_MEM_REGION ioctl cannot encrypt memory in place.
>  		 * Make a copy if there's only one backing memory source.
>  		 */
> -		source_addr = mmap(NULL, size_to_load, PROT_READ | PROT_WRITE,
> -				   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> -		TEST_ASSERT(source_addr,
> -			    "Could not allocate memory for loading memory region");
> -
> -		memcpy(source_addr, (void *)hva, size_to_load);
> +		if (region->region.guest_memfd == -1) {
> +			source_addr = mmap(NULL, size_to_load, PROT_READ | PROT_WRITE,
> +					   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +			TEST_ASSERT(source_addr,
> +				    "Could not allocate memory for loading memory region");
> +
> +			memcpy(source_addr, (void *)hva, size_to_load);
> +			memset((void *)hva, 0, size_to_load);
> +		}
>  
>  		tdx_init_mem_region(vm, source_addr, gpa, size_to_load);
>  
> -		munmap(source_addr, size_to_load);
> +		if (region->region.guest_memfd == -1)
> +			munmap(source_addr, size_to_load);
>  	}
>  }
>  
> -- 
> 2.51.0.rc0.155.g4a0f42376b-goog
>