Re: [PATCH v4 10/10] KVM: selftests: Test disabling NX hugepages on a VM

From: David Matlack
Date: Mon Apr 11 2022 - 18:37:37 EST

On Mon, Apr 11, 2022 at 2:10 PM Ben Gardon <bgardon@xxxxxxxxxx> wrote:
>
> Add an argument to the NX huge pages test to test disabling the feature
> on a VM using the new capability.
>
> Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
> .../selftests/kvm/include/kvm_util_base.h | 2 +
> tools/testing/selftests/kvm/lib/kvm_util.c | 19 ++++++-
> .../selftests/kvm/x86_64/nx_huge_pages_test.c | 53 +++++++++++++++----
> 3 files changed, 64 insertions(+), 10 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index f9c2ac0a5b97..15f24be6d93f 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -412,4 +412,6 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name);
>
> uint32_t guest_get_vcpuid(void);
>
> +int vm_disable_nx_huge_pages(struct kvm_vm *vm);
> +
> #endif /* SELFTEST_KVM_UTIL_BASE_H */
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 833c7e63d62d..5fa5608eef03 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -112,6 +112,15 @@ int vm_check_cap(struct kvm_vm *vm, long cap)
> return ret;
> }
>
> +static int __vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap)
> +{
> + int ret;
> +
> + ret = ioctl(vm->fd, KVM_ENABLE_CAP, cap);
> +
> + return ret;
> +}
> +
> /* VM Enable Capability
> *
> * Input Args:
> @@ -128,7 +137,7 @@ int vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap)
> {
> int ret;
>
> - ret = ioctl(vm->fd, KVM_ENABLE_CAP, cap);
> + ret = __vm_enable_cap(vm, cap);
> TEST_ASSERT(ret == 0, "KVM_ENABLE_CAP IOCTL failed,\n"
> " rc: %i errno: %i", ret, errno);
>
> @@ -2662,3 +2671,11 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name)
> stat_name, ret);
> return data;
> }
> +
> +int vm_disable_nx_huge_pages(struct kvm_vm *vm)
> +{
> + struct kvm_enable_cap cap = { 0 };
> +
> + cap.cap = KVM_CAP_VM_DISABLE_NX_HUGE_PAGES;
> + return __vm_enable_cap(vm, &cap);
> +}
> 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
> index 3f21726b22c7..f8edf7910950 100644
> --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> @@ -13,6 +13,8 @@
> #include <fcntl.h>
> #include <stdint.h>
> #include <time.h>
> +#include <linux/reboot.h>
> +#include <sys/syscall.h>
>
> #include <test_util.h>
> #include "kvm_util.h"
> @@ -77,14 +79,41 @@ static void check_split_count(struct kvm_vm *vm, int expected_splits)
> expected_splits, actual_splits);
> }
>
> -int main(int argc, char **argv)
> +void run_test(bool disable_nx)
> {
> struct kvm_vm *vm;
> struct timespec ts;
> void *hva;
> + int r;
>
> vm = vm_create_default(0, 0, guest_code);
>
> + if (disable_nx) {
> + kvm_check_cap(KVM_CAP_VM_DISABLE_NX_HUGE_PAGES);
> +
> + /*
> + * Check if this process has the reboot permissions needed to
> + * disable NX huge pages on a VM.
> + *
> + * The reboot call below will never have any effect because
> + * the magic values are not set correctly, however the
> + * permission check is done before the magic value check.
> + */
> + r = syscall(SYS_reboot, 0, 0, 0, NULL);
> + if (errno == EPERM) {

Should this be:

if (r && errno == EPERM) {

?

Otherwise errno might contain a stale value.

> + r = vm_disable_nx_huge_pages(vm);
> + TEST_ASSERT(r == EPERM,

TEST_ASSERT(r && errno == EPERM,

> + "This process should not have permission to disable NX huge pages");
> + return;
> + }
> +
> + TEST_ASSERT(errno == EINVAL,

r && errno == EINVAL ?

> + "Reboot syscall should fail with -EINVAL");
> +
> + r = vm_disable_nx_huge_pages(vm);
> + TEST_ASSERT(!r, "Disabling NX huge pages should not fail if process has reboot permissions");

nit: s/not fail/succeed/

> + }
> +
> vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
> HPAGE_GPA, HPAGE_SLOT,
> HPAGE_SLOT_NPAGES, 0);
> @@ -118,21 +147,21 @@ int main(int argc, char **argv)
> * to be remapped at 4k.
> */
> vcpu_run(vm, 0);
> - check_2m_page_count(vm, 1);
> - check_split_count(vm, 1);
> + check_2m_page_count(vm, disable_nx ? 2 : 1);
> + check_split_count(vm, disable_nx ? 0 : 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);
> + check_2m_page_count(vm, disable_nx ? 3 : 1);
> + check_split_count(vm, disable_nx ? 0 : 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);
> + check_2m_page_count(vm, disable_nx ? 3 : 1);
> + check_split_count(vm, disable_nx ? 0 : 2);
>
> /*
> * Give recovery thread time to run. The wrapper script sets
> @@ -145,7 +174,7 @@ int main(int argc, char **argv)
> /*
> * Now that the reclaimer has run, all the split pages should be gone.
> */
> - check_2m_page_count(vm, 1);
> + check_2m_page_count(vm, disable_nx ? 3 : 1);
> check_split_count(vm, 0);
>
> /*
> @@ -153,10 +182,16 @@ int main(int argc, char **argv)
> * reading from it causes a huge page mapping to be installed.
> */
> vcpu_run(vm, 0);
> - check_2m_page_count(vm, 2);
> + check_2m_page_count(vm, disable_nx ? 3 : 2);
> check_split_count(vm, 0);
>
> kvm_vm_free(vm);
> +}
> +
> +int main(int argc, char **argv)
> +{
> + run_test(false);
> + run_test(true);
>
> return 0;
> }
> --
> 2.35.1.1178.g4f1659d476-goog
>