Message-ID: <9079a7e7-17e6-72eb-3510-b07a60ce78df@amd.com>
Date: Fri, 23 Aug 2024 17:16:36 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Pratik R. Sampat" <pratikrajesh.sampat@....com>, kvm@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, pgonda@...gle.com,
 michael.roth@....com, shuah@...nel.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 8/9] KVM: selftests: Add a CoCo-specific test for
 KVM_PRE_FAULT_MEMORY

On 8/23/24 15:23, Pratik R. Sampat wrote:
> 
> 
> On 8/16/2024 2:23 PM, Pratik R. Sampat wrote:
>> From: Michael Roth <michael.roth@....com>
>>
>> SEV, SEV-ES, and SNP have a few corner cases where there is potential
>> for KVM_PRE_FAULT_MEMORY to behave differently depending on when it is
>> issued during initial guest setup. Exercising these various paths
>> requires a bit more fine-grained control over when the
>> KVM_PRE_FAULT_MEMORY requests are issued while setting up the guests.
>>
>> Since these CoCo-specific events are likely to be architecture-specific
>> KST helpers, take the existing generic test in pre_fault_memory_test.c
>> as a starting template, and then introduce an x86-specific version of
>> it with expanded coverage for SEV, SEV-ES, and SNP.
>>
>> Since there's a reasonable chance that TDX could extend this for similar
>> testing of TDX, give it a "coco-" prefix rather than an SEV-specific
>> one.
>>
>> Signed-off-by: Michael Roth <michael.roth@....com>
>> Co-developed-by: Pratik R. Sampat <pratikrajesh.sampat@....com>
>> Signed-off-by: Pratik R. Sampat <pratikrajesh.sampat@....com>
>> ---
>>  tools/testing/selftests/kvm/Makefile          |   1 +
>>  .../kvm/x86_64/coco_pre_fault_memory_test.c   | 314 ++++++++++++++++++
>>  2 files changed, 315 insertions(+)
>>  create mode 100644 tools/testing/selftests/kvm/x86_64/coco_pre_fault_memory_test.c
>>
>> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
>> index 48d32c5aa3eb..65d19b277b06 100644
>> --- a/tools/testing/selftests/kvm/Makefile
>> +++ b/tools/testing/selftests/kvm/Makefile
>> @@ -129,6 +129,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/amx_test
>>  TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test
>>  TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test
>>  TEST_GEN_PROGS_x86_64 += x86_64/recalc_apic_map_test
>> +TEST_GEN_PROGS_x86_64 += x86_64/coco_pre_fault_memory_test
>>  TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
>>  TEST_GEN_PROGS_x86_64 += demand_paging_test
>>  TEST_GEN_PROGS_x86_64 += dirty_log_test
>> diff --git a/tools/testing/selftests/kvm/x86_64/coco_pre_fault_memory_test.c b/tools/testing/selftests/kvm/x86_64/coco_pre_fault_memory_test.c
>> new file mode 100644
>> index 000000000000..e16fe185fb5a
>> --- /dev/null
>> +++ b/tools/testing/selftests/kvm/x86_64/coco_pre_fault_memory_test.c
>> @@ -0,0 +1,314 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +#include <linux/sizes.h>
>> +
>> +#include <test_util.h>
>> +#include <kvm_util.h>
>> +#include <processor.h>
>> +#include "sev.h"
>> +
>> +/* Arbitrarily chosen values */
>> +#define TEST_SIZE		(SZ_2M + PAGE_SIZE)
>> +#define TEST_NPAGES		(TEST_SIZE / PAGE_SIZE)
>> +#define TEST_SLOT		10
>> +#define TEST_GPA		0x100000000ul
>> +#define TEST_GVA		0x100000000ul
>> +
>> +enum prefault_snp_test_type {
>> +	/* Skip pre-faulting tests. */
>> +	NO_PREFAULT_TYPE = 0,
>> +	/*
>> +	 * Issue KVM_PRE_FAULT_MEMORY for GFNs mapping non-private memory
>> +	 * before finalizing the initial guest contents (e.g. via
>> +	 * KVM_SEV_SNP_LAUNCH_FINISH for SNP guests).
>> +	 *
>> +	 * This should result in failure since KVM explicitly disallows
>> +	 * KVM_PRE_FAULT_MEMORY from being issued prior to finalizing the
>> +	 * initial guest contents.
>> +	 */
>> +	PREFAULT_SHARED_BEFORE_FINALIZING = 0,
> 
> Just spotted that I have initialized both NO_PREFAULT_TYPE and
> PREFAULT_SHARED_BEFORE_FINALIZING to 0, effectively running the latter
> test type twice. I will fix in the next iteration that I post.

Enums start at 0, so you can just eliminate the assignments.

Thanks,
Tom

> 
> Thanks!
> Pratik
> 
>> +	/*
>> +	 * Issue KVM_PRE_FAULT_MEMORY for GFNs mapping private memory
>> +	 * before finalizing the initial guest contents (e.g. via
>> +	 * KVM_SEV_SNP_LAUNCH_FINISH for SNP guests).
>> +	 *
>> +	 * This should result in failure since KVM explicitly disallows
>> +	 * KVM_PRE_FAULT_MEMORY from being issued prior to finalizing the
>> +	 * initial guest contents.
>> +	 */
>> +	PREFAULT_PRIVATE_BEFORE_FINALIZING,
>> +	/*
>> +	 * Issue KVM_PRE_FAULT_MEMORY for GFNs mapping shared/private
>> +	 * memory after finalizing the initial guest contents
>> +	 * (e.g. via * KVM_SEV_SNP_LAUNCH_FINISH for SNP guests).
>> +	 *
>> +	 * This should succeed since pre-faulting is supported for both
>> +	 * non-private/private memory once the guest contents are finalized.
>> +	 */
>> +	PREFAULT_PRIVATE_SHARED_AFTER_FINALIZING
>> +};
>> +
>> +static void guest_code_sev(void)
>> +{
>> +	int i;
>> +
>> +	GUEST_ASSERT(rdmsr(MSR_AMD64_SEV) & MSR_AMD64_SEV_ENABLED);
>> +
>> +	for (i = 0; i < TEST_NPAGES; i++) {
>> +		uint64_t *src = (uint64_t *)(TEST_GVA + i * PAGE_SIZE);
>> +		uint64_t val = *src;
>> +
>> +		/* Validate the data stored in the pages */
>> +		if ((i < TEST_NPAGES / 2 && val != i + 1) ||
>> +		    (i >= TEST_NPAGES / 2 && val != 0)) {
>> +			GUEST_FAIL("Inconsistent view of memory values in guest");
>> +		}
>> +	}
>> +
>> +	if (rdmsr(MSR_AMD64_SEV) & MSR_AMD64_SEV_ES_ENABLED) {
>> +		wrmsr(MSR_AMD64_SEV_ES_GHCB, GHCB_MSR_TERM_REQ);
>> +		__asm__ __volatile__("rep; vmmcall");
>> +		GUEST_FAIL("This should be unreachable.");
>> +	}
>> +
>> +	GUEST_DONE();
>> +}
>> +
>> +static void __pre_fault_memory(struct kvm_vcpu *vcpu, u64 gpa, u64 size,
>> +			       u64 left, bool expect_fail)
>> +{
>> +	struct kvm_pre_fault_memory range = {
>> +		.gpa = gpa,
>> +		.size = size,
>> +		.flags = 0,
>> +	};
>> +	int ret, save_errno;
>> +	u64 prev;
>> +
>> +	do {
>> +		prev = range.size;
>> +		ret = __vcpu_ioctl(vcpu, KVM_PRE_FAULT_MEMORY, &range);
>> +		save_errno = errno;
>> +		TEST_ASSERT((range.size < prev) ^ (ret < 0),
>> +			    "%sexpecting range.size to change on %s",
>> +			    ret < 0 ? "not " : "",
>> +			    ret < 0 ? "failure" : "success");
>> +	} while (ret >= 0 ? range.size : save_errno == EINTR);
>> +
>> +	TEST_ASSERT(expect_fail ? !(range.size == left) : (range.size == left),
>> +		    "[EXPECT %s] completed with %lld bytes left, expected %" PRId64,
>> +		    expect_fail ? "FAIL" : "PASS",
>> +		    range.size, left);
>> +
>> +	if (left == 0) {
>> +		TEST_ASSERT(expect_fail ? ret : !ret,
>> +			    "[EXPECT %s] KVM_PRE_FAULT_MEMORY",
>> +			    expect_fail ? "FAIL" : "PASS");
>> +	} else {
>> +		/*
>> +		 * For shared memory, no memory slot causes RET_PF_EMULATE. It
>> +		 * results in -ENOENT.
>> +		 *
>> +		 * For private memory, no memory slot is an error case returning
>> +		 * -EFAULT, but it also possible the only the GPA ranges backed
>> +		 *  by a slot are marked as private, in which case the noslot
>> +		 *  range will also result in -ENOENT.
>> +		 *
>> +		 *  So allow both errors for now, but in the future it would be
>> +		 *  good to distinguish between these cases to tighten up the
>> +		 *  error-checking.
>> +		 */
>> +		TEST_ASSERT(expect_fail ? !ret :
>> +			    (ret && (save_errno == EFAULT || save_errno == ENOENT)),
>> +			    "[EXPECT %s] KVM_PRE_FAULT_MEMORY",
>> +			    expect_fail ? "FAIL" : "PASS");
>> +	}
>> +}
>> +
>> +static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 gpa,
>> +			     u64 size, u64 left)
>> +{
>> +	__pre_fault_memory(vcpu, gpa, size, left, false);
>> +}
>> +
>> +static void pre_fault_memory_negative(struct kvm_vcpu *vcpu, u64 gpa,
>> +				      u64 size, u64 left)
>> +{
>> +	__pre_fault_memory(vcpu, gpa, size, left, true);
>> +}
>> +
>> +static void pre_fault_memory_snp(struct kvm_vcpu *vcpu, struct kvm_vm *vm,
>> +				 bool private, enum prefault_snp_test_type p_type)
>> +{
>> +	if (p_type == PREFAULT_SHARED_BEFORE_FINALIZING)
>> +		pre_fault_memory_negative(vcpu, TEST_GPA, SZ_2M, 0);
>> +
>> +	snp_vm_launch_start(vm, SNP_POLICY);
>> +
>> +	if (p_type == PREFAULT_SHARED_BEFORE_FINALIZING)
>> +		pre_fault_memory_negative(vcpu, TEST_GPA, SZ_2M, 0);
>> +
>> +	if (private) {
>> +		/*
>> +		 * Make sure when pages are pre-faulted later after
>> +		 * finalization they are treated the same as a private
>> +		 * access by the guest so that the expected gmem
>> +		 * backing pages are used.
>> +		 */
>> +		vm_mem_set_private(vm, TEST_GPA, TEST_SIZE);
>> +		if (p_type == PREFAULT_PRIVATE_BEFORE_FINALIZING)
>> +			pre_fault_memory_negative(vcpu, TEST_GPA, SZ_2M, 0);
>> +	} else {
>> +		if (p_type == PREFAULT_SHARED_BEFORE_FINALIZING)
>> +			pre_fault_memory_negative(vcpu, TEST_GPA, SZ_2M, 0);
>> +	}
>> +
>> +	snp_vm_launch_update(vm);
>> +
>> +	if (p_type == PREFAULT_SHARED_BEFORE_FINALIZING)
>> +		pre_fault_memory_negative(vcpu, TEST_GPA, SZ_2M, 0);
>> +
>> +	snp_vm_launch_finish(vm);
>> +
>> +	/*
>> +	 * After finalization, pre-faulting either private or shared
>> +	 * ranges should work regardless of whether the pages were
>> +	 * encrypted as part of setting up initial guest state.
>> +	 */
>> +	if (p_type == PREFAULT_PRIVATE_SHARED_AFTER_FINALIZING) {
>> +		pre_fault_memory(vcpu, TEST_GPA, SZ_2M, 0);
>> +		pre_fault_memory(vcpu, TEST_GPA + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
>> +		pre_fault_memory(vcpu, TEST_GPA + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
>> +	}
>> +}
>> +
>> +static void pre_fault_memory_sev(unsigned long vm_type, struct kvm_vcpu *vcpu,
>> +				 struct kvm_vm *vm)
>> +{
>> +	uint32_t policy = (vm_type == KVM_X86_SEV_ES_VM) ? SEV_POLICY_ES : 0;
>> +
>> +	pre_fault_memory(vcpu, TEST_GPA, SZ_2M, 0);
>> +	pre_fault_memory(vcpu, TEST_GPA + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
>> +	pre_fault_memory(vcpu, TEST_GPA + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
>> +
>> +	sev_vm_launch(vm, policy);
>> +
>> +	pre_fault_memory(vcpu, TEST_GPA, SZ_2M, 0);
>> +	pre_fault_memory(vcpu, TEST_GPA + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
>> +	pre_fault_memory(vcpu, TEST_GPA + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
>> +
>> +	sev_vm_launch_measure(vm, alloca(256));
>> +
>> +	pre_fault_memory(vcpu, TEST_GPA, SZ_2M, 0);
>> +	pre_fault_memory(vcpu, TEST_GPA + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
>> +	pre_fault_memory(vcpu, TEST_GPA + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
>> +
>> +	sev_vm_launch_finish(vm);
>> +
>> +	pre_fault_memory(vcpu, TEST_GPA, SZ_2M, 0);
>> +	pre_fault_memory(vcpu, TEST_GPA + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
>> +	pre_fault_memory(vcpu, TEST_GPA + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
>> +}
>> +
>> +static void test_pre_fault_memory_sev(unsigned long vm_type, bool private,
>> +				      enum prefault_snp_test_type p_type)
>> +{
>> +	struct kvm_vcpu *vcpu;
>> +	struct kvm_vm *vm;
>> +	struct ucall uc;
>> +	int i;
>> +
>> +	vm = vm_sev_create_with_one_vcpu(vm_type, guest_code_sev, &vcpu);
>> +
>> +	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
>> +				    TEST_GPA, TEST_SLOT, TEST_NPAGES,
>> +				    (vm_type == KVM_X86_SNP_VM) ? KVM_MEM_GUEST_MEMFD : 0);
>> +
>> +	/*
>> +	 * Make sure guest page table is in agreement with what pages will be
>> +	 * initially encrypted by the ASP.
>> +	 */
>> +	if (private)
>> +		vm_mem_set_protected(vm, TEST_SLOT, TEST_GPA, TEST_NPAGES);
>> +
>> +	virt_map(vm, TEST_GVA, TEST_GPA, TEST_NPAGES);
>> +
>> +	/*
>> +	 * Populate the pages to compare data read from the guest
>> +	 * Populate the first half with data and second half as all zeros.
>> +	 */
>> +	for (i = 0; i < TEST_NPAGES; i++) {
>> +		uint64_t *hva = addr_gva2hva(vm, TEST_GVA + i * PAGE_SIZE);
>> +
>> +		if (i < TEST_NPAGES / 2)
>> +			*hva = i + 1;
>> +		else
>> +			*hva = 0;
>> +	}
>> +
>> +	if (vm_type == KVM_X86_SNP_VM)
>> +		pre_fault_memory_snp(vcpu, vm, private, p_type);
>> +	else
>> +		pre_fault_memory_sev(vm_type, vcpu, vm);
>> +
>> +	vcpu_run(vcpu);
>> +
>> +	if (vm->type == KVM_X86_SEV_ES_VM || vm->type == KVM_X86_SNP_VM) {
>> +		TEST_ASSERT(vcpu->run->exit_reason == KVM_EXIT_SYSTEM_EVENT,
>> +			    "Wanted SYSTEM_EVENT, got %s",
>> +			    exit_reason_str(vcpu->run->exit_reason));
>> +		TEST_ASSERT_EQ(vcpu->run->system_event.type, KVM_SYSTEM_EVENT_SEV_TERM);
>> +		TEST_ASSERT_EQ(vcpu->run->system_event.ndata, 1);
>> +		TEST_ASSERT_EQ(vcpu->run->system_event.data[0], GHCB_MSR_TERM_REQ);
>> +		goto out;
>> +	}
>> +
>> +	switch (get_ucall(vcpu, &uc)) {
>> +	case UCALL_DONE:
>> +		break;
>> +	case UCALL_ABORT:
>> +		REPORT_GUEST_ASSERT(uc);
>> +	default:
>> +		TEST_FAIL("Unexpected exit: %s",
>> +			  exit_reason_str(vcpu->run->exit_reason));
>> +	}
>> +
>> +out:
>> +	kvm_vm_free(vm);
>> +}
>> +
>> +static void test_pre_fault_memory(unsigned long vm_type, bool private)
>> +{
>> +	int pt;
>> +
>> +	if (vm_type && !(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type))) {
>> +		pr_info("Skipping tests for vm_type 0x%lx\n", vm_type);
>> +		return;
>> +	}
>> +
>> +	switch (vm_type) {
>> +	case KVM_X86_SEV_VM:
>> +	case KVM_X86_SEV_ES_VM:
>> +		test_pre_fault_memory_sev(vm_type, private, NO_PREFAULT_TYPE);
>> +		break;
>> +	case KVM_X86_SNP_VM:
>> +		for (pt = 0; pt <= PREFAULT_PRIVATE_SHARED_AFTER_FINALIZING; pt++)
>> +			test_pre_fault_memory_sev(vm_type, private, pt);
>> +		break;
>> +	default:
>> +		abort();
>> +	}
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +	TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
>> +
>> +	test_pre_fault_memory(KVM_X86_SEV_VM, false);
>> +	test_pre_fault_memory(KVM_X86_SEV_VM, true);
>> +	test_pre_fault_memory(KVM_X86_SEV_ES_VM, false);
>> +	test_pre_fault_memory(KVM_X86_SEV_ES_VM, true);
>> +	test_pre_fault_memory(KVM_X86_SNP_VM, false);
>> +	test_pre_fault_memory(KVM_X86_SNP_VM, true);
>> +
>> +	return 0;
>> +}
> 

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