On Mon, Jun 24, 2024 at 09:53:57AM -0400, Audra Mitchell wrote:
On Fri, Jun 21, 2024 at 05:27:43PM -0400, Peter Xu wrote:
On Fri, Jun 21, 2024 at 02:12:24PM -0400, Audra Mitchell wrote:
If CONFIG_PTE_MARKER_UFFD_WP is disabled, then testing with test_uffdio_up
Here you're talking about pte markers, then..
enables calling uffdio_regsiter with the flag UFFDIO_REGISTER_MODE_WP. The kernel ensures in vma_can_userfault() that if CONFIG_PTE_MARKER_UFFD_WP is disabled, only allow the VM_UFFD_WP on anonymous vmas.
Signed-off-by: Audra Mitchell audra@redhat.com
tools/testing/selftests/mm/uffd-stress.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c index b9b6d858eab8..2601c9dfadd6 100644 --- a/tools/testing/selftests/mm/uffd-stress.c +++ b/tools/testing/selftests/mm/uffd-stress.c @@ -419,6 +419,9 @@ static void parse_test_type_arg(const char *raw_type) test_uffdio_wp = test_uffdio_wp && (features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
- if (test_type != TEST_ANON && !(features & UFFD_FEATURE_WP_UNPOPULATED))
test_uffdio_wp = false;... here you're checking against wp_unpopulated. I'm slightly confused.
Are you running this test over shmem/hugetlb when the WP feature isn't supported?
I'm wondering whether you're looking for UFFD_FEATURE_WP_HUGETLBFS_SHMEM instead.
I can confirm, its all really confusing... So in userfaultfd_api, we disable three features if CONFIG_PTE_MARKER_UFFD_WP is not enabled- including UFFD_FEATURE_WP_UNPOPULATED:
#ifndef CONFIG_PTE_MARKER_UFFD_WP uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM; uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED; uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC; #endif
If you run the userfaultfd selftests with the run_vmtests script we get several failures stemming from trying to call uffdio_regsiter with the flag UFFDIO_REGISTER_MODE_WP. However, the kernel ensures in vma_can_userfault() that if CONFIG_PTE_MARKER_UFFD_WP is disabled, only allow the VM_UFFD_WP - which is set when you pass the UFFDIO_REGISTER_MODE_WP flag - on anonymous vmas.
In parse_test_type_arg() I added the features check against UFFD_FEATURE_WP_UNPOPULATED as it seemed the most well know feature/flag. I'm more than happy to take any suggestions and adapt them if you have any!
There're documents for these features in the headers:
* UFFD_FEATURE_WP_HUGETLBFS_SHMEM indicates that userfaultfd * write-protection mode is supported on both shmem and hugetlbfs. * * UFFD_FEATURE_WP_UNPOPULATED indicates that userfaultfd * write-protection mode will always apply to unpopulated pages * (i.e. empty ptes). This will be the default behavior for shmem * & hugetlbfs, so this flag only affects anonymous memory behavior * when userfault write-protection mode is registered.
While in this context ("test_type != TEST_ANON") IIUC the accurate feature to check is UFFD_FEATURE_WP_HUGETLBFS_SHMEM.
In most kernels they should behave the same indeed, but note that since UNPOPULATED was introduced later than shmem/hugetlb support, it means on some kernel the result of checking these two features will be different.
Thanks,