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Message-ID: <CANgfPd9zbKx655-m=jkN4kC4v8LBr5DY+5=wa1L=fAftkjmp_A@mail.gmail.com>
Date: Thu, 7 Apr 2022 11:39:31 -0700
From: Ben Gardon <bgardon@...gle.com>
To: David Matlack <dmatlack@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
David Dunn <daviddunn@...gle.com>,
Jing Zhang <jingzhangos@...gle.com>,
Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH v3 11/11] selftests: KVM: Test disabling NX hugepages on a VM
On Thu, Apr 7, 2022 at 11:26 AM Ben Gardon <bgardon@...gle.com> wrote:
>
> On Tue, Apr 5, 2022 at 3:55 PM David Matlack <dmatlack@...gle.com> wrote:
> >
> > On Wed, Mar 30, 2022 at 10:46:21AM -0700, Ben Gardon 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@...gle.com>
> > > ---
> > > .../selftests/kvm/include/kvm_util_base.h | 2 +
> > > tools/testing/selftests/kvm/lib/kvm_util.c | 7 ++
> > > .../selftests/kvm/x86_64/nx_huge_pages_test.c | 67 ++++++++++++++++---
> > > .../kvm/x86_64/nx_huge_pages_test.sh | 2 +-
> > > 4 files changed, 66 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > > index 72163ba2f878..4db8251c3ce5 100644
> > > --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> > > +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > > @@ -411,4 +411,6 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name);
> > >
> > > uint32_t guest_get_vcpuid(void);
> > >
> > > +void 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 9d72d1bb34fa..46a7fa08d3e0 100644
> > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > > @@ -2765,3 +2765,10 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name)
> > > return value;
> > > }
> > >
> > > +void vm_disable_nx_huge_pages(struct kvm_vm *vm)
> > > +{
> > > + struct kvm_enable_cap cap = { 0 };
> > > +
> > > + cap.cap = KVM_CAP_VM_DISABLE_NX_HUGE_PAGES;
> > > + 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 2bcbe4efdc6a..a0c79f6ddc08 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"
> > > @@ -57,13 +59,56 @@ static void check_split_count(struct kvm_vm *vm, int expected_splits)
> > > expected_splits, actual_splits);
> > > }
> > >
> > > +static void help(void)
> > > +{
> > > + puts("");
> > > + printf("usage: nx_huge_pages_test.sh [-x]\n");
> > > + puts("");
> > > + printf(" -x: Allow executable huge pages on the VM.\n");
> >
> > Making it a flag means we won't exercise it by default. Is there are
> > reason to avoid exercising KVM_CAP_VM_DISABLE_NX_HUGE_PAGES by default?
> >
> > Assuming no, I would recommend factoring out the test to a helper
> > function that takes a parameter that tells it if nx_huge_pages is
> > enabled or disabled. Then run this helper function multiple times. E.g.
> > once with nx_huge_pages enabled, once with nx_huge_pages disabled via
> > KVM_CAP_VM_DISABLE_NX_HUGE_PAGES. This would also then let you test that
> > disabling via module param also works.
> >
> > By the way, that brings up another issue. What if NX HugePages is not
> > enabled on this host? e.g. we're running on AMD, or we're running on a
> > non-affected Intel host, or we're running on a machine where nx huge
> > pages has been disabled by the admin? The test should probably return
> > KSFT_SKIP in those cases.
The wrapper script just always turns nx_huge_pages on, which I think
is a better solution, but perhaps it should check for permission
errors when doing that.
>
> That's all a good idea. Will do.
>
> >
> > > + puts("");
> > > + exit(0);
> > > +}
> > > +
> > > int main(int argc, char **argv)
> > > {
> > > struct kvm_vm *vm;
> > > struct timespec ts;
> > > + bool disable_nx = false;
> > > + int opt;
> > > + int r;
> > > +
> > > + while ((opt = getopt(argc, argv, "x")) != -1) {
> > > + switch (opt) {
> > > + case 'x':
> > > + disable_nx = true;
> > > + break;
> > > + case 'h':
> > > + default:
> > > + help();
> > > + break;
> > > + }
> > > + }
> > >
> > > vm = vm_create(VM_MODE_DEFAULT, DEFAULT_GUEST_PHY_PAGES, O_RDWR);
> > >
> > > + if (disable_nx) {
> > > + /*
> > > + * 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 (r == -EPERM)
> > > + return KSFT_SKIP;
> > > + TEST_ASSERT(r == -EINVAL,
> > > + "Reboot syscall should fail with -EINVAL");
> >
> > Just check if KVM_CAP_VM_DISABLE_NX_HUGE_PAGES returns -EPERM?
We could do that but then we wouldn't be checking that the permission
checks work as expected.
> >
> > > +
> > > + vm_disable_nx_huge_pages(vm);
> > > + }
> > > +
> > > vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
> > > HPAGE_PADDR_START, HPAGE_SLOT,
> > > HPAGE_SLOT_NPAGES, 0);
> > > @@ -83,21 +128,21 @@ int main(int argc, char **argv)
> > > * at 2M.
> > > */
> > > run_guest_code(vm, guest_code0);
> > > - check_2m_page_count(vm, 2);
> > > - check_split_count(vm, 2);
> > > + check_2m_page_count(vm, disable_nx ? 4 : 2);
> > > + check_split_count(vm, disable_nx ? 0 : 2);
> > >
> > > /*
> > > * guest_code1 is in the same huge page as data1, so it will cause
> > > * that huge page to be remapped at 4k.
> > > */
> > > run_guest_code(vm, guest_code1);
> > > - check_2m_page_count(vm, 1);
> > > - check_split_count(vm, 3);
> > > + check_2m_page_count(vm, disable_nx ? 4 : 1);
> > > + check_split_count(vm, disable_nx ? 0 : 3);
> > >
> > > /* Run guest_code0 again to check that is has no effect. */
> > > run_guest_code(vm, guest_code0);
> > > - check_2m_page_count(vm, 1);
> > > - check_split_count(vm, 3);
> > > + check_2m_page_count(vm, disable_nx ? 4 : 1);
> > > + check_split_count(vm, disable_nx ? 0 : 3);
> > >
> > > /*
> > > * Give recovery thread time to run. The wrapper script sets
> > > @@ -110,7 +155,7 @@ 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 ? 4 : 1);
> > > check_split_count(vm, 0);
> > >
> > > /*
> > > @@ -118,13 +163,13 @@ int main(int argc, char **argv)
> > > * again to check that pages are mapped at 2M again.
> > > */
> > > run_guest_code(vm, guest_code0);
> > > - check_2m_page_count(vm, 2);
> > > - check_split_count(vm, 2);
> > > + check_2m_page_count(vm, disable_nx ? 4 : 2);
> > > + check_split_count(vm, disable_nx ? 0 : 2);
> > >
> > > /* Pages are once again split from running guest_code1. */
> > > run_guest_code(vm, guest_code1);
> > > - check_2m_page_count(vm, 1);
> > > - check_split_count(vm, 3);
> > > + check_2m_page_count(vm, disable_nx ? 4 : 1);
> > > + check_split_count(vm, disable_nx ? 0 : 3);
> > >
> > > kvm_vm_free(vm);
> > >
> > > 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
> > > index 19fc95723fcb..29f999f48848 100755
> > > --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > > @@ -14,7 +14,7 @@ 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
> > > +./nx_huge_pages_test "${@}"
> > > RET=$?
> > >
> > > echo $NX_HUGE_PAGES > /sys/module/kvm/parameters/nx_huge_pages
> > > --
> > > 2.35.1.1021.g381101b075-goog
> > >
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