Re: [PATCH v2 8/9] KVM: selftests: Add a CoCo-specific test for KVM_PRE_FAULT_MEMORY

From: Pratik R. Sampat
Date: Mon Aug 26 2024 - 18:02:29 EST

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On 8/23/2024 5:16 PM, Tom Lendacky wrote:
> 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@xxxxxxx>
>>>
>>> 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@xxxxxxx>
>>> Co-developed-by: Pratik R. Sampat <pratikrajesh.sampat@xxxxxxx>
>>> Signed-off-by: Pratik R. Sampat <pratikrajesh.sampat@xxxxxxx>
>>> ---
>>> 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.
>

Ack. I Will get rid of it here and the next patch as well.

Thanks!

> 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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