Re: [PATCH v2] tools/mm: add hwpoison-panic tool

On 2026/8/3 19:31, Breno Leitao wrote:
> Add a tool that enables the vm.panic_on_unrecoverable_memory_failure
> sysctl, picks a kernel-owned PFN and writes its physical address to
> hard_offline_page.  Three page kinds are selectable with -k: rodata
> (default), slab or pgtable. In all cases the host should panic.
> 
> Example:
> 
>         # ./hwpoison-panic -k slab --yes-panic-my-kernel
>         injecting hwpoison at phys 0x100032000 (pfn 0x100032, kind=slab)
>         expecting kernel panic: 'Memory failure: <pfn>: unrecoverable page'
> 
> In dmesg, you will see:
> 
>         Memory failure: 0x100032: unhandlable page.
>         Memory failure: 0x100032: recovery action for reserved kernel page: Ignored
>         Kernel panic - not syncing: Memory failure: 0x100032: unrecoverable page
> 
> This lives in tools/mm rather than selftests/mm because every successful
> run crashes the machine, which is not something to run from CI.
> 
> The --yes-panic-my-kernel argument is required so an accidental
> invocation does not take the box down.
> 
> Signed-off-by: Breno Leitao <[email protected]>

This patch looks good to me with some nits below.

> ---
> Changes in v2:
> - Reword the file header, the tool triggers a panic rather than
>   confirming one (SJ Park)
> - Rename -f to --yes-panic-my-kernel and say in usage() what it costs
>   (SJ Park)
> - Call check_prereqs() before getpagesize() (SJ Park)
> - Use 64-bit types for physical addresses and PFNs.  On a 32-bit build
>   the old long/unsigned long pair truncated addresses above 4G, and the
>   negative error sentinel was indistinguishable from a valid address at
>   or above 2G
> - Link to v1: https://patch.msgid.link/20260731-memory_failure_rewrite_test-v1-1-6aa8c6435693@debian.org
...
> +
> +static int pick_kpageflags_phys_addr(uint64_t want, uint64_t *phys_addr)
> +{
> +	uint64_t pfn = (16UL << 20) / page_size;

Could we use SZ_16M macro here?

> +	uint64_t flags;
> +	int ret = -1;
> +	int fd;
> +
> +	fd = open(PROC_KPAGEFLAGS, O_RDONLY);
> +	if (fd < 0)
> +		return -1;
> +
> +	for (; kpageflags_read(fd, pfn, &flags) == 0; pfn++) {
> +		if ((flags & want) && !(flags & BIT(HWPOISON)) &&
> +		    !(flags & BIT(NOPAGE)) && !(flags & BIT(COMPOUND_TAIL))) {
> +			*phys_addr = pfn * page_size;
> +			ret = 0;
> +			break;
> +		}
> +	}
> +
> +	close(fd);
> +	return ret;
> +}
> +
> +static int read_sysctl(unsigned long *val)
> +{
> +	FILE *f = fopen(SYSCTL_PATH, "r");
> +	int ret;
> +
> +	if (!f)
> +		return -1;
> +	ret = fscanf(f, "%lu", val) == 1 ? 0 : -1;
> +	fclose(f);
> +
> +	return ret;
> +}
> +
> +static int write_sysctl(unsigned long val)
> +{
> +	FILE *f = fopen(SYSCTL_PATH, "w");
> +	int ret;
> +
> +	if (!f)
> +		return -1;
> +	ret = fprintf(f, "%lu", val) < 0 ? -1 : 0;
> +	fclose(f);
> +
> +	return ret;
> +}
> +
> +/* hard_offline_page() injects with MF_SW_SIMULATED, so unpoison is allowed. */
> +static void unpoison_pfn(uint64_t pfn)
> +{
> +	char path[PATH_MAX], buf[32];
> +	const char *debugfs;
> +	int fd, len;
> +
> +	debugfs = debugfs__mount();

I might be miss something but I can't find the implementation of debugfs__mount.

> +	if (!debugfs)
> +		return;
> +
> +	snprintf(path, sizeof(path), "%s/hwpoison/unpoison-pfn", debugfs);
> +	fd = open(path, O_WRONLY);
> +	if (fd < 0)
> +		return;
> +
> +	len = snprintf(buf, sizeof(buf), "0x%llx\n", (unsigned long long)pfn);
> +	if (write(fd, buf, len) < 0)
> +		perror("unpoison-pfn");
> +	close(fd);
> +}
> +
...
> +
> +static void check_prereqs(int armed)
> +{
> +	if (geteuid())
> +		fatal("must run as root\n");
> +	if (access(SYSCTL_PATH, W_OK))
> +		fatal("%s not present (kernel without the sysctl?)\n",
> +		      SYSCTL_PATH);
> +	if (access(INJECT_PATH, W_OK))
> +		fatal("%s not present (no MEMORY_HOTPLUG?)\n", INJECT_PATH);

MEMORY_HOTPLUG?

Thanks.
.

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