Re: [PATCH 2/2] selftests/mm: check that PAGEMAP_SCAN returns correct categories

[Ryan Roberts]

On 06/11/2023 22:09, Andrei Vagin wrote:
> Right now, tests read page flags from /proc/pid/pagemap files. With this
> change, tests will check that PAGEMAP_SCAN return correct information
> too.
> 
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
> ---
>  tools/testing/selftests/mm/vm_util.c | 53 ++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 3082b40492dd..ec3478b96e4c 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -4,6 +4,7 @@
>  #include <dirent.h>
>  #include <sys/ioctl.h>
>  #include <linux/userfaultfd.h>
> +#include <linux/fs.h>
>  #include <sys/syscall.h>
>  #include <unistd.h>
>  #include "../kselftest.h"
> @@ -28,19 +29,65 @@ uint64_t pagemap_get_entry(int fd, char *start)
>  	return entry;
>  }
>  
> +static uint64_t pagemap_scan_get_categories(int fd, char *start)
> +{
> +	struct pm_scan_arg arg;
> +	struct page_region r;
> +	long ret;
> +
> +	arg.start = (uintptr_t)start;
> +	arg.end = (uintptr_t)(start + psize());
> +	arg.vec = (uintptr_t)&r;
> +	arg.vec_len = 1;
> +	arg.flags = 0;
> +	arg.size = sizeof(struct pm_scan_arg);
> +	arg.max_pages = 0;
> +	arg.category_inverted = 0;
> +	arg.category_mask = 0;
> +	arg.category_anyof_mask = PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | PAGE_IS_FILE |
> +				  PAGE_IS_PRESENT | PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |
> +				  PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY;
> +	arg.return_mask = arg.category_anyof_mask;
> +
> +	ret = ioctl(fd, PAGEMAP_SCAN, &arg);
> +	if (ret < 0)
> +		ksft_exit_fail_msg("PAGEMAP_SCAN failed: %s\n", strerror(errno));

FYI, when run against kernel v6.7-rc1, this fails with EINVAL. I'm guessing
you've added this as part of testing an extension to this ABI and its only
present in mm-unstable?

I believe that normally we try to keep selftests backwards compatible so they
run on older kernels (a feature I rely on). As a result 3 or so test suites are
immediately failing (inc cow). Can this be fixed to fallback to old behaviour
gracefully in this case?

Thanks,
Ryan


> +	if (ret == 0)
> +		return 0;
> +	return r.categories;
> +}
> +
> +static bool page_entry_is(int fd, char *start, char *desc,
> +			  uint64_t pagemap_flags, uint64_t pagescan_flags)
> +{
> +	bool m, s;
> +
> +	m = pagemap_get_entry(fd, start) & pagemap_flags;
> +	s = pagemap_scan_get_categories(fd, start) & pagescan_flags;
> +	if (m == s)
> +		return m;
> +
> +	ksft_exit_fail_msg(
> +		"read and ioctl return unmatched results for %s: %d %d", desc, m, s);
> +	return m;
> +}
> +
>  bool pagemap_is_softdirty(int fd, char *start)
>  {
> -	return pagemap_get_entry(fd, start) & PM_SOFT_DIRTY;
> +	return page_entry_is(fd, start, "soft-dirty",
> +				PM_SOFT_DIRTY, PAGE_IS_SOFT_DIRTY);
>  }
>  
>  bool pagemap_is_swapped(int fd, char *start)
>  {
> -	return pagemap_get_entry(fd, start) & PM_SWAP;
> +	return page_entry_is(fd, start, "swap", PM_SWAP, PAGE_IS_SWAPPED);
>  }
>  
>  bool pagemap_is_populated(int fd, char *start)
>  {
> -	return pagemap_get_entry(fd, start) & (PM_PRESENT | PM_SWAP);
> +	return page_entry_is(fd, start, "populated",
> +				PM_PRESENT | PM_SWAP,
> +				PAGE_IS_PRESENT | PAGE_IS_SWAPPED);
>  }
>  
>  unsigned long pagemap_get_pfn(int fd, char *start)