linux-kernel - Re: [PATCH v2 8/8] selftests/mm: report SKIP in pfnmap if a check fails

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Message-ID: <09c214df-c3aa-48e4-9587-c54c667c6ce9@kernel.org>
Date: Mon, 19 Jan 2026 12:16:24 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Mark Brown
 <broonie@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 8/8] selftests/mm: report SKIP in pfnmap if a check
 fails

On 1/7/26 17:48, Kevin Brodsky wrote:
> pfnmap currently checks the target file in FIXTURE_SETUP(pfnmap),
> meaning once for every test, and skips the test if any check fails.
> 
> The target file is the same for every test so this is a little
> overkill. More importantly, this approach means that the whole suite
> will report PASS even if all the tests are skipped because kernel
> configuration (e.g. CONFIG_STRICT_DEVMEM=y) prevented /dev/mem from
> being mapped, for instance.
> 
> Let's ensure that KSFT_SKIP is returned as exit code if any check
> fails by performing the checks in pfnmap_init(), run once. That
> function also takes care of finding the offset of the pages to be
> mapped and saves it in a global. The file is still mapped/unmapped
> for every test, as some of them modify the mapping.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> ---
>   tools/testing/selftests/mm/pfnmap.c | 81 ++++++++++++++++++++---------
>   1 file changed, 55 insertions(+), 26 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/pfnmap.c b/tools/testing/selftests/mm/pfnmap.c
> index 35b0e3ed54cd..e41d5464130b 100644
> --- a/tools/testing/selftests/mm/pfnmap.c
> +++ b/tools/testing/selftests/mm/pfnmap.c
> @@ -25,8 +25,11 @@
>   #include "kselftest_harness.h"
>   #include "vm_util.h"
>   
> +#define DEV_MEM_NPAGES	2
> +
>   static sigjmp_buf sigjmp_buf_env;
>   static char *file = "/dev/mem";
> +static off_t file_offset;
>   
>   static void signal_handler(int sig)
>   {
> @@ -88,7 +91,7 @@ static int find_ram_target(off_t *offset,
>   			break;
>   
>   		/* We need two pages. */
> -		if (end > start + 2 * pagesize) {
> +		if (end > start + DEV_MEM_NPAGES * pagesize) {
>   			fclose(file);
>   			*offset = start;
>   			return 0;
> @@ -97,9 +100,49 @@ static int find_ram_target(off_t *offset,
>   	return -ENOENT;
>   }
>   
> +static void pfnmap_init(void)
> +{
> +	size_t pagesize = getpagesize();
> +	size_t size = DEV_MEM_NPAGES * pagesize;
> +	int fd;
> +	void *addr;
> +
> +	if (strncmp(file, "/dev/mem", strlen("/dev/mem")) == 0) {
> +		int err = find_ram_target(&file_offset, pagesize);
> +
> +		if (err)
> +			ksft_exit_skip("Cannot find ram target in '/proc/iomem': %s\n",
> +				       strerror(-err));
> +	} else {
> +		file_offset = 0;
> +	}
> +
> +	/*
> +	 * Make sure we can open and map the file, and perform some basic
> +	 * checks; skip the whole suite if anything goes wrong.
> +	 * A fresh mapping is then created for every test case by
> +	 * FIXTURE_SETUP(pfnmap).
> +	 */
> +	fd = open(file, O_RDONLY);
> +	if (fd < 0)
> +		ksft_exit_skip("Cannot open '%s': %s\n", file, strerror(errno));
> +
> +	addr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, file_offset);
> +	if (addr == MAP_FAILED)
> +		ksft_exit_skip("Cannot mmap '%s': %s\n", file, strerror(errno));
> +
> +	if (!check_vmflag_pfnmap(addr))
> +		ksft_exit_skip("Invalid file: '%s'. Not pfnmap'ed\n", file);
> +
> +	if (test_read_access(addr, size))
> +		ksft_exit_skip("Cannot read-access mmap'ed '%s'\n", file);
> +
> +	munmap(addr, size);

Why not keep the fd open then and supply that to all tests without the 
need for them to open/close?

Then, also the file cannot change etc.

-- 
Cheers

David