linux-kernel - Re: [PATCH v8 21/30] KVM: selftests: TDX: Verify the behavior when host consumes a TD private memory

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Message-ID: <fa61f808-ffd0-46cd-9e59-1a4e743bea24@linux.intel.com>
Date: Thu, 14 Aug 2025 19:17:06 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sagi Shahar <sagis@...gle.com>
Cc: 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>, Oliver Upton <oliver.upton@...ux.dev>,
 "Pratik R. Sampat" <pratikrajesh.sampat@....com>,
 Reinette Chatre <reinette.chatre@...el.com>, Ira Weiny
 <ira.weiny@...el.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 21/30] KVM: selftests: TDX: Verify the behavior when
 host consumes a TD private memory



On 8/8/2025 4:16 AM, Sagi Shahar wrote:
> From: Ryan Afranji <afranji@...gle.com>
>
> The test checks that host can only read fixed values when trying to
> access the guest's private memory.
>
> Signed-off-by: Ryan Afranji <afranji@...gle.com>
> Signed-off-by: Sagi Shahar <sagis@...gle.com>
> ---
>   tools/testing/selftests/kvm/x86/tdx_vm_test.c | 83 ++++++++++++++++++-
>   1 file changed, 82 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kvm/x86/tdx_vm_test.c b/tools/testing/selftests/kvm/x86/tdx_vm_test.c
> index 2f75f12d2a44..b6ef0348746c 100644
> --- a/tools/testing/selftests/kvm/x86/tdx_vm_test.c
> +++ b/tools/testing/selftests/kvm/x86/tdx_vm_test.c
> @@ -959,6 +959,85 @@ void verify_td_cpuid_tdcall(void)
>   	printf("\t ... PASSED\n");
>   }
>   
> +/*
> + * Shared variables between guest and host for host reading private mem test
> + */
> +static uint64_t tdx_test_host_read_private_mem_addr;
> +#define TDX_HOST_READ_PRIVATE_MEM_PORT_TEST 0x53
> +
> +void guest_host_read_priv_mem(void)
> +{
> +	uint64_t placeholder = 0;
> +	uint64_t ret;
> +
> +	/* Set value */
> +	*((uint32_t *)tdx_test_host_read_private_mem_addr) = 0xABCD;
> +
> +	/* Exit so host can read value */
> +	ret = tdg_vp_vmcall_instruction_io(TDX_HOST_READ_PRIVATE_MEM_PORT_TEST,
> +					   4, PORT_WRITE, &placeholder);
> +	tdx_assert_error(ret);
> +
> +	/* Update guest_var's value and have host reread it. */
> +	*((uint32_t *)tdx_test_host_read_private_mem_addr) = 0xFEDC;
> +
> +	tdx_test_success();
> +}
> +
> +void verify_host_reading_private_mem(void)
> +{
> +	uint64_t second_host_read;
> +	uint64_t first_host_read;
> +	struct kvm_vcpu *vcpu;
> +	vm_vaddr_t test_page;
> +	uint64_t *host_virt;
> +	struct kvm_vm *vm;
> +
> +	vm = td_create();
> +	td_initialize(vm, VM_MEM_SRC_ANONYMOUS, 0);
> +	vcpu = td_vcpu_add(vm, 0, guest_host_read_priv_mem);
> +
> +	test_page = vm_vaddr_alloc_page(vm);
> +	TEST_ASSERT(test_page < BIT_ULL(32),
> +		    "Test address should fit in 32 bits so it can be sent to the guest");

I didn't understand it.
Could you elaborate a bit?

> +
> +	host_virt = addr_gva2hva(vm, test_page);
> +	TEST_ASSERT(host_virt,
> +		    "Guest address not found in guest memory regions\n");
> +
> +	tdx_test_host_read_private_mem_addr = test_page;
> +	sync_global_to_guest(vm, tdx_test_host_read_private_mem_addr);
> +
> +	td_finalize(vm);
> +
> +	printf("Verifying host's behavior when reading TD private memory:\n");

When the host accesses host_virt, it's not accessing the same page of the
private page of the TD, so it's not accurate to say the host is reading or
consuming TD private memory.

> +
> +	tdx_run(vcpu);
> +	tdx_test_assert_io(vcpu, TDX_HOST_READ_PRIVATE_MEM_PORT_TEST,
> +			   4, PORT_WRITE);
> +	printf("\t ... Guest's variable contains 0xABCD\n");
> +
> +	/* Host reads guest's variable. */
> +	first_host_read = *host_virt;
> +	printf("\t ... Host's read attempt value: %lu\n", first_host_read);
> +
> +	/* Guest updates variable and host rereads it. */
> +	tdx_run(vcpu);
> +	printf("\t ... Guest's variable updated to 0xFEDC\n");
> +
> +	second_host_read = *host_virt;
> +	printf("\t ... Host's second read attempt value: %lu\n",
> +	       second_host_read);
> +
> +	TEST_ASSERT(first_host_read == second_host_read,
> +		    "Host did not read a fixed pattern\n");
> +
> +	printf("\t ... Fixed pattern was returned to the host\n");
> +
> +	kvm_vm_free(vm);
> +	printf("\t ... PASSED\n");
> +}
> +
>   int main(int argc, char **argv)
>   {
>   	ksft_print_header();
> @@ -966,7 +1045,7 @@ int main(int argc, char **argv)
>   	if (!is_tdx_enabled())
>   		ksft_exit_skip("TDX is not supported by the KVM. Exiting.\n");
>   
> -	ksft_set_plan(13);
> +	ksft_set_plan(14);
>   	ksft_test_result(!run_in_new_process(&verify_td_lifecycle),
>   			 "verify_td_lifecycle\n");
>   	ksft_test_result(!run_in_new_process(&verify_report_fatal_error),
> @@ -993,6 +1072,8 @@ int main(int argc, char **argv)
>   			 "verify_mmio_writes\n");
>   	ksft_test_result(!run_in_new_process(&verify_td_cpuid_tdcall),
>   			 "verify_td_cpuid_tdcall\n");
> +	ksft_test_result(!run_in_new_process(&verify_host_reading_private_mem),
> +			 "verify_host_reading_private_mem\n");
>   
>   	ksft_finished();
>   	return 0;