Re: [PATCH v4 05/10] KVM: selftests: Add NX huge pages test

[David Matlack <dmatlack@google.com>]

On Mon, Apr 11, 2022 at 2:10 PM Ben Gardon <bgardon@google.com> wrote:
>
> There's currently no test coverage of NX hugepages in KVM selftests, so
> add a basic test to ensure that the feature works as intended.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  tools/testing/selftests/kvm/Makefile          |  10 ++
>  .../selftests/kvm/include/kvm_util_base.h     |   1 +
>  tools/testing/selftests/kvm/lib/kvm_util.c    |  48 ++++++
>  .../selftests/kvm/x86_64/nx_huge_pages_test.c | 163 ++++++++++++++++++
>  .../kvm/x86_64/nx_huge_pages_test.sh          |  25 +++
>  5 files changed, 247 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
>  create mode 100755 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
>
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index af582d168621..9bb9bce4df37 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -43,6 +43,10 @@ LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handler
>  LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
>  LIBKVM_riscv = lib/riscv/processor.c lib/riscv/ucall.c
>
> +# Non-compiled test targets
> +TEST_PROGS_x86_64 += x86_64/nx_huge_pages_test.sh
> +
> +# Compiled test targets
>  TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
>  TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
>  TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
> @@ -104,6 +108,9 @@ TEST_GEN_PROGS_x86_64 += steal_time
>  TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test
>  TEST_GEN_PROGS_x86_64 += system_counter_offset_test
>
> +# Compiled outputs used by test targets
> +TEST_GEN_PROGS_EXTENDED_x86_64 += x86_64/nx_huge_pages_test
> +
>  TEST_GEN_PROGS_aarch64 += aarch64/arch_timer
>  TEST_GEN_PROGS_aarch64 += aarch64/debug-exceptions
>  TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list
> @@ -142,7 +149,9 @@ TEST_GEN_PROGS_riscv += kvm_page_table_test
>  TEST_GEN_PROGS_riscv += set_memory_region_test
>  TEST_GEN_PROGS_riscv += kvm_binary_stats_test
>
> +TEST_PROGS += $(TEST_PROGS_$(UNAME_M))
>  TEST_GEN_PROGS += $(TEST_GEN_PROGS_$(UNAME_M))
> +TEST_GEN_PROGS_EXTENDED += $(TEST_GEN_PROGS_EXTENDED_$(UNAME_M))
>  LIBKVM += $(LIBKVM_$(UNAME_M))
>
>  INSTALL_HDR_PATH = $(top_srcdir)/usr
> @@ -193,6 +202,7 @@ $(OUTPUT)/libkvm.a: $(LIBKVM_OBJS)
>  x := $(shell mkdir -p $(sort $(dir $(TEST_GEN_PROGS))))
>  all: $(STATIC_LIBS)
>  $(TEST_GEN_PROGS): $(STATIC_LIBS)
> +$(TEST_GEN_PROGS_EXTENDED): $(STATIC_LIBS)
>
>  cscope: include_paths = $(LINUX_TOOL_INCLUDE) $(LINUX_HDR_PATH) include lib ..
>  cscope:
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index b2684cfc2cb1..f9c2ac0a5b97 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -408,6 +408,7 @@ void read_vm_stats_desc(int stats_fd, struct kvm_stats_header *header,
>  int read_stat_data(int stats_fd, struct kvm_stats_header *header,
>                    struct kvm_stats_desc *desc, uint64_t *data,
>                    ssize_t max_elements);
> +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name);
>
>  uint32_t guest_get_vcpuid(void);
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 64e2085f1129..833c7e63d62d 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -2614,3 +2614,51 @@ int read_stat_data(int stats_fd, struct kvm_stats_header *header,
>
>         return ret;
>  }
> +
> +static int vm_get_stat_data(struct kvm_vm *vm, const char *stat_name,
> +                           uint64_t *data, ssize_t max_elements)
> +{
> +       struct kvm_stats_desc *stats_desc;
> +       struct kvm_stats_header header;
> +       struct kvm_stats_desc *desc;
> +       size_t size_desc;
> +       int stats_fd;
> +       int ret = -EINVAL;
> +       int i;
> +
> +       stats_fd = vm_get_stats_fd(vm);
> +
> +       read_vm_stats_header(stats_fd, &header);
> +
> +       stats_desc = alloc_vm_stats_desc(stats_fd, &header);
> +       read_vm_stats_desc(stats_fd, &header, stats_desc);

This is a fair bit of redundant work to do when reading every stat.
Reading stats in selftests is probably not going to be
performance-senstive, but it should be pretty easy to move everything
above to VM initialization and storing the outputs in struct kvm_vm
for access during this function.

> +
> +       size_desc = sizeof(struct kvm_stats_desc) + header.name_size;
> +
> +       /* Read kvm stats data one by one */
> +       for (i = 0; i < header.num_desc; ++i) {
> +               desc = (void *)stats_desc + (i * size_desc);
> +
> +               if (strcmp(desc->name, stat_name))
> +                       continue;
> +
> +               ret = read_stat_data(stats_fd, &header, desc, data,
> +                                    max_elements);
> +       }
> +
> +       free(stats_desc);
> +       close(stats_fd);
> +       return ret;
> +}
> +
> +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name)

nit: I'd prefer the simpler "vm_get_stat()". The function signature
already makes it clear we're reading one stat value. And when we add
more support for more complicated stats (e.g.
vm_get_histogram_stat()), I think "vm_get_stat()" will still work for
reading single value stats.

> +{
> +       uint64_t data;
> +       int ret;
> +
> +       ret = vm_get_stat_data(vm, stat_name, &data, 1);
> +       TEST_ASSERT(ret == 1,
> +                   "Stat %s expected to have 1 element, but %d returned",
> +                   stat_name, ret);
> +       return data;
> +}
> diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> new file mode 100644
> index 000000000000..3f21726b22c7
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> @@ -0,0 +1,163 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * tools/testing/selftests/kvm/nx_huge_page_test.c
> + *
> + * Usage: to be run via nx_huge_page_test.sh, which does the necessary
> + * environment setup and teardown
> + *
> + * Copyright (C) 2022, Google LLC.
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <fcntl.h>
> +#include <stdint.h>
> +#include <time.h>
> +
> +#include <test_util.h>
> +#include "kvm_util.h"
> +
> +#define HPAGE_SLOT             10
> +#define HPAGE_GVA              (23*1024*1024)
> +#define HPAGE_GPA              (10*1024*1024)
> +#define HPAGE_SLOT_NPAGES      (512 * 3)
> +#define PAGE_SIZE              4096
> +
> +/*
> + * When writing to guest memory, write the opcode for the `ret` instruction so
> + * that subsequent iteractions can exercise instruction fetch by calling the
> + * memory.

I think this comment needs to be reworded to better fit this test.


> + */
> +#define RETURN_OPCODE 0xC3
> +
> +void guest_code(void)
> +{
> +       uint64_t hpage_1 = HPAGE_GVA;
> +       uint64_t hpage_2 = hpage_1 + (PAGE_SIZE * 512);
> +       uint64_t hpage_3 = hpage_2 + (PAGE_SIZE * 512);
> +
> +       READ_ONCE(*(uint64_t *)hpage_1);
> +       GUEST_SYNC(1);
> +
> +       READ_ONCE(*(uint64_t *)hpage_2);
> +       GUEST_SYNC(2);
> +
> +       ((void (*)(void)) hpage_1)();
> +       GUEST_SYNC(3);
> +
> +       ((void (*)(void)) hpage_3)();
> +       GUEST_SYNC(4);
> +
> +       READ_ONCE(*(uint64_t *)hpage_1);
> +       GUEST_SYNC(5);
> +
> +       READ_ONCE(*(uint64_t *)hpage_3);
> +       GUEST_SYNC(6);
> +}
> +
> +static void check_2m_page_count(struct kvm_vm *vm, int expected_pages_2m)
> +{
> +       int actual_pages_2m;
> +
> +       actual_pages_2m = vm_get_single_stat(vm, "pages_2m");
> +
> +       TEST_ASSERT(actual_pages_2m == expected_pages_2m,
> +                   "Unexpected 2m page count. Expected %d, got %d",
> +                   expected_pages_2m, actual_pages_2m);
> +}
> +
> +static void check_split_count(struct kvm_vm *vm, int expected_splits)
> +{
> +       int actual_splits;
> +
> +       actual_splits = vm_get_single_stat(vm, "nx_lpage_splits");
> +
> +       TEST_ASSERT(actual_splits == expected_splits,
> +                   "Unexpected nx lpage split count. Expected %d, got %d",
> +                   expected_splits, actual_splits);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +       struct kvm_vm *vm;
> +       struct timespec ts;
> +       void *hva;
> +
> +       vm = vm_create_default(0, 0, guest_code);
> +
> +       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
> +                                   HPAGE_GPA, HPAGE_SLOT,
> +                                   HPAGE_SLOT_NPAGES, 0);
> +
> +       virt_map(vm, HPAGE_GVA, HPAGE_GPA, HPAGE_SLOT_NPAGES);
> +
> +       hva = addr_gpa2hva(vm, HPAGE_GPA);
> +       memset(hva, RETURN_OPCODE, HPAGE_SLOT_NPAGES * PAGE_SIZE);
> +
> +       check_2m_page_count(vm, 0);
> +       check_split_count(vm, 0);
> +
> +       /*
> +        * The guest code will first read from the first hugepage, resulting
> +        * in a huge page mapping being created.
> +        */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 1);
> +       check_split_count(vm, 0);
> +
> +       /*
> +        * Then the guest code will read from the second hugepage, resulting
> +        * in another huge page mapping being created.
> +        */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 2);
> +       check_split_count(vm, 0);
> +
> +       /*
> +        * Next, the guest will execute from the first huge page, causing it
> +        * to be remapped at 4k.
> +        */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 1);
> +       check_split_count(vm, 1);
> +
> +       /*
> +        * Executing from the third huge page (previously unaccessed) will
> +        * cause part to be mapped at 4k.
> +        */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 1);
> +       check_split_count(vm, 2);
> +
> +       /* Reading from the first huge page again should have no effect. */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 1);
> +       check_split_count(vm, 2);
> +
> +       /*
> +        * Give recovery thread time to run. The wrapper script sets
> +        * recovery_period_ms to 100, so wait 5x that.
> +        */
> +       ts.tv_sec = 0;
> +       ts.tv_nsec = 500000000;
> +       nanosleep(&ts, NULL);
> +
> +       /*
> +        * Now that the reclaimer has run, all the split pages should be gone.
> +        */
> +       check_2m_page_count(vm, 1);
> +       check_split_count(vm, 0);
> +
> +       /*
> +        * The 4k mapping on hpage 3 should have been removed, so check that
> +        * reading from it causes a huge page mapping to be installed.
> +        */
> +       vcpu_run(vm, 0);
> +       check_2m_page_count(vm, 2);
> +       check_split_count(vm, 0);
> +
> +       kvm_vm_free(vm);
> +
> +       return 0;
> +}
> +
> diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> new file mode 100755
> index 000000000000..19fc95723fcb
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> @@ -0,0 +1,25 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only */
> +
> +# tools/testing/selftests/kvm/nx_huge_page_test.sh
> +# Copyright (C) 2022, Google LLC.
> +
> +NX_HUGE_PAGES=$(cat /sys/module/kvm/parameters/nx_huge_pages)
> +NX_HUGE_PAGES_RECOVERY_RATIO=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio)
> +NX_HUGE_PAGES_RECOVERY_PERIOD=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms)
> +HUGE_PAGES=$(cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages)
> +
> +echo 1 > /sys/module/kvm/parameters/nx_huge_pages
> +echo 1 > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> +echo 100 > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> +echo 200 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> +
> +./nx_huge_pages_test
> +RET=$?
> +
> +echo $NX_HUGE_PAGES > /sys/module/kvm/parameters/nx_huge_pages
> +echo $NX_HUGE_PAGES_RECOVERY_RATIO > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> +echo $NX_HUGE_PAGES_RECOVERY_PERIOD > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> +echo $HUGE_PAGES > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> +
> +exit $RET
> --
> 2.35.1.1178.g4f1659d476-goog
>