Re: [RFC PATCH v5 23/29] KVM: selftests: TDX: Add shared memory test

On Fri, Mar 01, 2024 at 08:02:43PM +0800, Yan Zhao wrote:

...

+void guest_shared_mem(void) +{

• uint32_t *test_mem_shared_gva =

• (uint32_t *)TDX_SHARED_MEM_TEST_SHARED_GVA;
  

• uint64_t placeholder;
• uint64_t ret;
• /* Map gpa as shared */
• ret = tdg_vp_vmcall_map_gpa(test_mem_shared_gpa, PAGE_SIZE,

• 		    &placeholder);
  

• if (ret)

• tdx_test_fatal_with_data(ret, __LINE__);
  

• *test_mem_shared_gva = TDX_SHARED_MEM_TEST_GUEST_WRITE_VALUE;
• /* Exit so host can read shared value */
• ret = tdg_vp_vmcall_instruction_io(TDX_SHARED_MEM_TEST_INFO_PORT, 4,

• 			   TDG_VP_VMCALL_INSTRUCTION_IO_WRITE,
  

• 			   &placeholder);
  

• if (ret)

• tdx_test_fatal_with_data(ret, __LINE__);
  

• /* Read value written by host and send it back out for verification */
• ret = tdg_vp_vmcall_instruction_io(TDX_SHARED_MEM_TEST_INFO_PORT, 4,

• 			   TDG_VP_VMCALL_INSTRUCTION_IO_WRITE,
  

• 			   (uint64_t *)test_mem_shared_gva);
  

• if (ret)

• tdx_test_fatal_with_data(ret, __LINE__);
  

+}

+int verify_shared_mem(void) +{

• struct kvm_vm *vm;
• struct kvm_vcpu *vcpu;
• vm_vaddr_t test_mem_private_gva;
• uint32_t *test_mem_hva;
• vm = td_create();
• td_initialize(vm, VM_MEM_SRC_ANONYMOUS, 0);
• vcpu = td_vcpu_add(vm, 0, guest_shared_mem);
• /*

• * Set up shared memory page for testing by first allocating as private
  

• * and then mapping the same GPA again as shared. This way, the TD does
  

• * not have to remap its page tables at runtime.
  

• */
  

• test_mem_private_gva = vm_vaddr_alloc(vm, vm->page_size,

• 			      TDX_SHARED_MEM_TEST_PRIVATE_GVA);
  

• TEST_ASSERT_EQ(test_mem_private_gva, TDX_SHARED_MEM_TEST_PRIVATE_GVA);
• test_mem_hva = addr_gva2hva(vm, test_mem_private_gva);
• TEST_ASSERT(test_mem_hva != NULL,

•     "Guest address not found in guest memory regions\n");
  

• test_mem_private_gpa = addr_gva2gpa(vm, test_mem_private_gva);
• virt_pg_map_shared(vm, TDX_SHARED_MEM_TEST_SHARED_GVA,

• 	   test_mem_private_gpa);
  

• test_mem_shared_gpa = test_mem_private_gpa | BIT_ULL(vm->pa_bits - 1);
• sync_global_to_guest(vm, test_mem_private_gpa);
• sync_global_to_guest(vm, test_mem_shared_gpa);
• td_finalize(vm);
• printf("Verifying shared memory accesses for TDX\n");
• /* Begin guest execution; guest writes to shared memory. */
• printf("\t ... Starting guest execution\n");
• /* Handle map gpa as shared */
• td_vcpu_run(vcpu);
• TDX_TEST_CHECK_GUEST_FAILURE(vcpu);

The first VMExit should be caused by tdvmcall map gpa, so it's impossible to be guest failure.

Ah, if KVM has bugs and returns to guest's map gpa tdvmcall as error without exiting to user space, then it's possible to meet guest failure here.

Move this line TDX_TEST_CHECK_GUEST_FAILURE(vcpu) to after the next td_vcpu_run() is better.

So, looks it's required to be checked after every vcpu run. Without checking it (as in below), the selftest will not be able to print out the guest reported fatal error.

...

• td_vcpu_run(vcpu);
• TDX_TEST_ASSERT_IO(vcpu, TDX_SHARED_MEM_TEST_INFO_PORT, 4,

• 	   TDG_VP_VMCALL_INSTRUCTION_IO_WRITE);
  

• TEST_ASSERT_EQ(*test_mem_hva, TDX_SHARED_MEM_TEST_GUEST_WRITE_VALUE);
• *test_mem_hva = TDX_SHARED_MEM_TEST_HOST_WRITE_VALUE;
• td_vcpu_run(vcpu);
• TDX_TEST_ASSERT_IO(vcpu, TDX_SHARED_MEM_TEST_INFO_PORT, 4,

• 	   TDG_VP_VMCALL_INSTRUCTION_IO_WRITE);
  

• TEST_ASSERT_EQ(

• *(uint32_t *)((void *)vcpu->run + vcpu->run->io.data_offset),
  

• TDX_SHARED_MEM_TEST_HOST_WRITE_VALUE);
  

• printf("\t ... PASSED\n");
• kvm_vm_free(vm);
• return 0;

+}