[RFC PATCH v12 29/33] KVM: selftests: Add x86-only selftest for private memory conversions
Sean Christopherson
seanjc at google.com
Wed Sep 13 18:55:27 PDT 2023
From: Vishal Annapurve <vannapurve at google.com>
Add a selftest to exercise implicit/explicit conversion functionality
within KVM and verify:
- Shared memory is visible to host userspace
- Private memory is not visible to host userspace
- Host userspace and guest can communicate over shared memory
- Data in shared backing is preserved across conversions (test's
host userspace doesn't free the data)
- Private memory is bound to the lifetime of the VM
Ideally, KVM's selftests infrastructure would be reworked to allow backing
a single region of guest memory with multiple memslots for _all_ backing
types and shapes, i.e. ideally the code for using a single backing fd
across multiple memslots would work for "regular" memory as well. But
sadly, support for KVM_CREATE_GUEST_MEMFD has languished for far too long,
and overhauling selftests' memslots infrastructure would likely open a can
of worms, i.e. delay things even further.
Signed-off-by: Vishal Annapurve <vannapurve at google.com>
Co-developed-by: Ackerley Tng <ackerleytng at google.com>
Signed-off-by: Ackerley Tng <ackerleytng at google.com>
Co-developed-by: Sean Christopherson <seanjc at google.com>
Signed-off-by: Sean Christopherson <seanjc at google.com>
---
tools/testing/selftests/kvm/Makefile | 1 +
.../kvm/x86_64/private_mem_conversions_test.c | 410 ++++++++++++++++++
2 files changed, 411 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index a3bb36fb3cfc..b709a52d5cdb 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -81,6 +81,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
TEST_GEN_PROGS_x86_64 += x86_64/nested_exceptions_test
TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test
TEST_GEN_PROGS_x86_64 += x86_64/pmu_event_filter_test
+TEST_GEN_PROGS_x86_64 += x86_64/private_mem_conversions_test
TEST_GEN_PROGS_x86_64 += x86_64/set_boot_cpu_id
TEST_GEN_PROGS_x86_64 += x86_64/set_sregs_test
TEST_GEN_PROGS_x86_64 += x86_64/smaller_maxphyaddr_emulation_test
diff --git a/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
new file mode 100644
index 000000000000..50541246d6fd
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
@@ -0,0 +1,410 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022, Google LLC.
+ */
+#define _GNU_SOURCE /* for program_invocation_short_name */
+#include <fcntl.h>
+#include <limits.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include <linux/compiler.h>
+#include <linux/kernel.h>
+#include <linux/kvm_para.h>
+#include <linux/memfd.h>
+#include <linux/sizes.h>
+
+#include <test_util.h>
+#include <kvm_util.h>
+#include <processor.h>
+
+#define BASE_DATA_SLOT 10
+#define BASE_DATA_GPA ((uint64_t)(1ull << 32))
+#define PER_CPU_DATA_SIZE ((uint64_t)(SZ_2M + PAGE_SIZE))
+
+/* Horrific macro so that the line info is captured accurately :-( */
+#define memcmp_g(gpa, pattern, size) \
+do { \
+ uint8_t *mem = (uint8_t *)gpa; \
+ size_t i; \
+ \
+ for (i = 0; i < size; i++) \
+ __GUEST_ASSERT(mem[i] == pattern, \
+ "Expected 0x%x at offset %lu (gpa 0x%llx), got 0x%x", \
+ pattern, i, gpa + i, mem[i]); \
+} while (0)
+
+static void memcmp_h(uint8_t *mem, uint8_t pattern, size_t size)
+{
+ size_t i;
+
+ for (i = 0; i < size; i++)
+ TEST_ASSERT(mem[i] == pattern,
+ "Expected 0x%x at offset %lu, got 0x%x",
+ pattern, i, mem[i]);
+}
+
+/*
+ * Run memory conversion tests with explicit conversion:
+ * Execute KVM hypercall to map/unmap gpa range which will cause userspace exit
+ * to back/unback private memory. Subsequent accesses by guest to the gpa range
+ * will not cause exit to userspace.
+ *
+ * Test memory conversion scenarios with following steps:
+ * 1) Access private memory using private access and verify that memory contents
+ * are not visible to userspace.
+ * 2) Convert memory to shared using explicit conversions and ensure that
+ * userspace is able to access the shared regions.
+ * 3) Convert memory back to private using explicit conversions and ensure that
+ * userspace is again not able to access converted private regions.
+ */
+
+#define GUEST_STAGE(o, s) { .offset = o, .size = s }
+
+enum ucall_syncs {
+ SYNC_SHARED,
+ SYNC_PRIVATE,
+};
+
+static void guest_sync_shared(uint64_t gpa, uint64_t size,
+ uint8_t current_pattern, uint8_t new_pattern)
+{
+ GUEST_SYNC5(SYNC_SHARED, gpa, size, current_pattern, new_pattern);
+}
+
+static void guest_sync_private(uint64_t gpa, uint64_t size, uint8_t pattern)
+{
+ GUEST_SYNC4(SYNC_PRIVATE, gpa, size, pattern);
+}
+
+/* Arbitrary values, KVM doesn't care about the attribute flags. */
+#define MAP_GPA_SHARED BIT(0)
+#define MAP_GPA_DO_FALLOCATE BIT(1)
+
+static void guest_map_mem(uint64_t gpa, uint64_t size, bool map_shared,
+ bool do_fallocate)
+{
+ uint64_t flags = 0;
+
+ if (map_shared)
+ flags |= MAP_GPA_SHARED;
+ if (do_fallocate)
+ flags |= MAP_GPA_DO_FALLOCATE;
+ kvm_hypercall_map_gpa_range(gpa, size, flags);
+}
+
+static void guest_map_shared(uint64_t gpa, uint64_t size, bool do_fallocate)
+{
+ guest_map_mem(gpa, size, true, do_fallocate);
+}
+
+static void guest_map_private(uint64_t gpa, uint64_t size, bool do_fallocate)
+{
+ guest_map_mem(gpa, size, false, do_fallocate);
+}
+
+static void guest_run_test(uint64_t base_gpa, bool do_fallocate)
+{
+ struct {
+ uint64_t offset;
+ uint64_t size;
+ uint8_t pattern;
+ } stages[] = {
+ GUEST_STAGE(0, PAGE_SIZE),
+ GUEST_STAGE(0, SZ_2M),
+ GUEST_STAGE(PAGE_SIZE, PAGE_SIZE),
+ GUEST_STAGE(PAGE_SIZE, SZ_2M),
+ GUEST_STAGE(SZ_2M, PAGE_SIZE),
+ };
+ const uint8_t init_p = 0xcc;
+ uint64_t j;
+ int i;
+
+ /* Memory should be shared by default. */
+ memset((void *)base_gpa, ~init_p, PER_CPU_DATA_SIZE);
+ guest_sync_shared(base_gpa, PER_CPU_DATA_SIZE, (uint8_t)~init_p, init_p);
+ memcmp_g(base_gpa, init_p, PER_CPU_DATA_SIZE);
+
+ for (i = 0; i < ARRAY_SIZE(stages); i++) {
+ uint64_t gpa = base_gpa + stages[i].offset;
+ uint64_t size = stages[i].size;
+ uint8_t p1 = 0x11;
+ uint8_t p2 = 0x22;
+ uint8_t p3 = 0x33;
+ uint8_t p4 = 0x44;
+
+ /*
+ * Set the test region to pattern one to differentiate it from
+ * the data range as a whole (contains the initial pattern).
+ */
+ memset((void *)gpa, p1, size);
+
+ /*
+ * Convert to private, set and verify the private data, and
+ * then verify that the rest of the data (map shared) still
+ * holds the initial pattern, and that the host always sees the
+ * shared memory (initial pattern). Unlike shared memory,
+ * punching a hole in private memory is destructive, i.e.
+ * previous values aren't guaranteed to be preserved.
+ */
+ guest_map_private(gpa, size, do_fallocate);
+
+ if (size > PAGE_SIZE) {
+ memset((void *)gpa, p2, PAGE_SIZE);
+ goto skip;
+ }
+
+ memset((void *)gpa, p2, size);
+ guest_sync_private(gpa, size, p1);
+
+ /*
+ * Verify that the private memory was set to pattern two, and
+ * that shared memory still holds the initial pattern.
+ */
+ memcmp_g(gpa, p2, size);
+ if (gpa > base_gpa)
+ memcmp_g(base_gpa, init_p, gpa - base_gpa);
+ if (gpa + size < base_gpa + PER_CPU_DATA_SIZE)
+ memcmp_g(gpa + size, init_p,
+ (base_gpa + PER_CPU_DATA_SIZE) - (gpa + size));
+
+ /*
+ * Convert odd-number page frames back to shared to verify KVM
+ * also correctly handles holes in private ranges.
+ */
+ for (j = 0; j < size; j += PAGE_SIZE) {
+ if ((j >> PAGE_SHIFT) & 1) {
+ guest_map_shared(gpa + j, PAGE_SIZE, do_fallocate);
+ guest_sync_shared(gpa + j, PAGE_SIZE, p1, p3);
+
+ memcmp_g(gpa + j, p3, PAGE_SIZE);
+ } else {
+ guest_sync_private(gpa + j, PAGE_SIZE, p1);
+ }
+ }
+
+skip:
+ /*
+ * Convert the entire region back to shared, explicitly write
+ * pattern three to fill in the even-number frames before
+ * asking the host to verify (and write pattern four).
+ */
+ guest_map_shared(gpa, size, do_fallocate);
+ memset((void *)gpa, p3, size);
+ guest_sync_shared(gpa, size, p3, p4);
+ memcmp_g(gpa, p4, size);
+
+ /* Reset the shared memory back to the initial pattern. */
+ memset((void *)gpa, init_p, size);
+
+ /*
+ * Free (via PUNCH_HOLE) *all* private memory so that the next
+ * iteration starts from a clean slate, e.g. with respect to
+ * whether or not there are pages/folios in guest_mem.
+ */
+ guest_map_shared(base_gpa, PER_CPU_DATA_SIZE, true);
+ }
+}
+
+static void guest_code(uint64_t base_gpa)
+{
+ /*
+ * Run everything twice, with and without doing fallocate() on the
+ * guest_memfd backing when converting between shared and private.
+ */
+ guest_run_test(base_gpa, false);
+ guest_run_test(base_gpa, true);
+ GUEST_DONE();
+}
+
+static void handle_exit_hypercall(struct kvm_vcpu *vcpu)
+{
+ struct kvm_run *run = vcpu->run;
+ uint64_t gpa = run->hypercall.args[0];
+ uint64_t size = run->hypercall.args[1] * PAGE_SIZE;
+ bool map_shared = run->hypercall.args[2] & MAP_GPA_SHARED;
+ bool do_fallocate = run->hypercall.args[2] & MAP_GPA_DO_FALLOCATE;
+ struct kvm_vm *vm = vcpu->vm;
+
+ TEST_ASSERT(run->hypercall.nr == KVM_HC_MAP_GPA_RANGE,
+ "Wanted MAP_GPA_RANGE (%u), got '%llu'",
+ KVM_HC_MAP_GPA_RANGE, run->hypercall.nr);
+
+ if (do_fallocate)
+ vm_guest_mem_fallocate(vm, gpa, size, map_shared);
+
+ vm_set_memory_attributes(vm, gpa, size,
+ map_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE);
+ run->hypercall.ret = 0;
+}
+
+static bool run_vcpus;
+
+static void *__test_mem_conversions(void *__vcpu)
+{
+ struct kvm_vcpu *vcpu = __vcpu;
+ struct kvm_run *run = vcpu->run;
+ struct kvm_vm *vm = vcpu->vm;
+ struct ucall uc;
+
+ while (!READ_ONCE(run_vcpus))
+ ;
+
+ for ( ;; ) {
+ vcpu_run(vcpu);
+
+ if (run->exit_reason == KVM_EXIT_HYPERCALL) {
+ handle_exit_hypercall(vcpu);
+ continue;
+ }
+
+ TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+ "Wanted KVM_EXIT_IO, got exit reason: %u (%s)",
+ run->exit_reason, exit_reason_str(run->exit_reason));
+
+ switch (get_ucall(vcpu, &uc)) {
+ case UCALL_ABORT:
+ REPORT_GUEST_ASSERT(uc);
+ case UCALL_SYNC: {
+ uint8_t *hva = addr_gpa2hva(vm, uc.args[1]);
+ uint64_t size = uc.args[2];
+
+ TEST_ASSERT(uc.args[0] == SYNC_SHARED ||
+ uc.args[0] == SYNC_PRIVATE,
+ "Unknown sync command '%ld'", uc.args[0]);
+
+ /* In all cases, the host should observe the shared data. */
+ memcmp_h(hva, uc.args[3], size);
+
+ /* For shared, write the new pattern to guest memory. */
+ if (uc.args[0] == SYNC_SHARED)
+ memset(hva, uc.args[4], size);
+ break;
+ }
+ case UCALL_DONE:
+ return NULL;
+ default:
+ TEST_FAIL("Unknown ucall 0x%lx.", uc.cmd);
+ }
+ }
+}
+
+static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t nr_vcpus,
+ uint32_t nr_memslots)
+{
+ /*
+ * Allocate enough memory so that each vCPU's chunk of memory can be
+ * naturally aligned with respect to the size of the backing store.
+ */
+ const size_t size = align_up(PER_CPU_DATA_SIZE, get_backing_src_pagesz(src_type));
+ const size_t memfd_size = size * nr_vcpus;
+ struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ pthread_t threads[KVM_MAX_VCPUS];
+ uint64_t gmem_flags;
+ struct kvm_vm *vm;
+ int memfd, i, r;
+
+ const struct vm_shape shape = {
+ .mode = VM_MODE_DEFAULT,
+ .type = KVM_X86_SW_PROTECTED_VM,
+ };
+
+ vm = __vm_create_with_vcpus(shape, nr_vcpus, 0, guest_code, vcpus);
+
+ vm_enable_cap(vm, KVM_CAP_EXIT_HYPERCALL, (1 << KVM_HC_MAP_GPA_RANGE));
+
+ if (backing_src_can_be_huge(src_type))
+ gmem_flags = KVM_GUEST_MEMFD_ALLOW_HUGEPAGE;
+ else
+ gmem_flags = 0;
+ memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);
+
+ for (i = 0; i < nr_memslots; i++)
+ vm_mem_add(vm, src_type, BASE_DATA_GPA + size * i,
+ BASE_DATA_SLOT + i, size / vm->page_size,
+ KVM_MEM_PRIVATE, memfd, size * i);
+
+ for (i = 0; i < nr_vcpus; i++) {
+ uint64_t gpa = BASE_DATA_GPA + i * size;
+
+ vcpu_args_set(vcpus[i], 1, gpa);
+
+ virt_map(vm, gpa, gpa, size / vm->page_size);
+
+ pthread_create(&threads[i], NULL, __test_mem_conversions, vcpus[i]);
+ }
+
+ WRITE_ONCE(run_vcpus, true);
+
+ for (i = 0; i < nr_vcpus; i++)
+ pthread_join(threads[i], NULL);
+
+ kvm_vm_free(vm);
+
+ /*
+ * Allocate and free memory from the guest_memfd after closing the VM
+ * fd. The guest_memfd is gifted a reference to its owning VM, i.e.
+ * should prevent the VM from being fully destroyed until the last
+ * reference to the guest_memfd is also put.
+ */
+ r = fallocate(memfd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0, memfd_size);
+ TEST_ASSERT(!r, __KVM_SYSCALL_ERROR("fallocate()", r));
+
+ r = fallocate(memfd, FALLOC_FL_KEEP_SIZE, 0, memfd_size);
+ TEST_ASSERT(!r, __KVM_SYSCALL_ERROR("fallocate()", r));
+}
+
+static void usage(const char *cmd)
+{
+ puts("");
+ printf("usage: %s [-h] [-m] [-s mem_type] [-n nr_vcpus]\n", cmd);
+ puts("");
+ backing_src_help("-s");
+ puts("");
+ puts(" -n: specify the number of vcpus (default: 1)");
+ puts("");
+ puts(" -m: use multiple memslots (default: 1)");
+ puts("");
+}
+
+int main(int argc, char *argv[])
+{
+ enum vm_mem_backing_src_type src_type = DEFAULT_VM_MEM_SRC;
+ bool use_multiple_memslots = false;
+ uint32_t nr_vcpus = 1;
+ uint32_t nr_memslots;
+ int opt;
+
+ TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
+ TEST_REQUIRE(kvm_has_cap(KVM_CAP_EXIT_HYPERCALL));
+ TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));
+
+ while ((opt = getopt(argc, argv, "hms:n:")) != -1) {
+ switch (opt) {
+ case 's':
+ src_type = parse_backing_src_type(optarg);
+ break;
+ case 'n':
+ nr_vcpus = atoi_positive("nr_vcpus", optarg);
+ break;
+ case 'm':
+ use_multiple_memslots = true;
+ break;
+ case 'h':
+ default:
+ usage(argv[0]);
+ exit(0);
+ }
+ }
+
+ nr_memslots = use_multiple_memslots ? nr_vcpus : 1;
+
+ test_mem_conversions(src_type, nr_vcpus, nr_memslots);
+
+ return 0;
+}
--
2.42.0.283.g2d96d420d3-goog
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