[PATCH RESEND] x86/mtrr: Replace simple_strtoul with kstrtoul in parse_mtrr_spare_reg

[PATCH RESEND] x86/mtrr: Replace simple_strtoul with kstrtoul in parse_mtrr_spare_reg

[Thorsten Blum]

Replace simple_strtoul() with the recommended kstrtoul() for parsing the
'mtrr_spare_reg_nr' boot parameter.

Check the return value of kstrtoul() and reject invalid values. This
adds error handling while preserving behavior for existing values, and
removes use of the deprecated simple_strtoul() helper. The current code
silently sets 'nr_mtrr_spare_reg = 0' if parsing fails, instead of
leaving the default value (CONFIG_MTRR_SANITIZER_SPARE_REG_NR_DEFAULT)
unchanged.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 arch/x86/kernel/cpu/mtrr/cleanup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c
index 763534d77f59..1de5134b1916 100644
--- a/arch/x86/kernel/cpu/mtrr/cleanup.c
+++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
@@ -437,9 +437,7 @@ static unsigned long nr_mtrr_spare_reg __initdata =
 
 static int __init parse_mtrr_spare_reg(char *arg)
 {
-	if (arg)
-		nr_mtrr_spare_reg = simple_strtoul(arg, NULL, 0);
-	return 0;
+	return kstrtoul(arg, 0, &nr_mtrr_spare_reg);
 }
 early_param("mtrr_spare_reg_nr", parse_mtrr_spare_reg);
 
-- 
Thorsten Blum <thorsten.blum@linux.dev>
GPG: 1D60 735E 8AEF 3BE4 73B6  9D84 7336 78FD 8DFE EAD4

Re: [PATCH RESEND] x86/mtrr: Replace simple_strtoul with kstrtoul in parse_mtrr_spare_reg

[Borislav Petkov]

On Tue, Jan 27, 2026 at 10:58:23PM +0100, Thorsten Blum wrote:
> Replace simple_strtoul() with the recommended kstrtoul() for parsing the
> 'mtrr_spare_reg_nr' boot parameter.
> 
> Check the return value of kstrtoul() and reject invalid values.

Where?

> This adds error handling while preserving behavior for existing values, and

s/This adds/Add/

Describe your changes in imperative mood.

Also, pls read section "2) Describe your changes" in
Documentation/process/submitting-patches.rst for more details.

Also, see section "Changelog" in
Documentation/process/maintainer-tip.rst

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH RESEND] x86/mtrr: Replace simple_strtoul with kstrtoul in parse_mtrr_spare_reg

[Thorsten Blum]

On 28. Feb 2026, at 15:58, Borislav Petkov wrote:
> On Tue, Jan 27, 2026 at 10:58:23PM +0100, Thorsten Blum wrote:
>> Replace simple_strtoul() with the recommended kstrtoul() for parsing the
>> 'mtrr_spare_reg_nr' boot parameter.
>> 
>> Check the return value of kstrtoul() and reject invalid values.
> 
> Where?

The check is implicit in the return statement. Previously,
parse_mtrr_spare_reg() always returned 0 (success). Returning kstrtoul()
directly propagates 0 on success and -errno on failure, which adds
proper error handling.

However, I realized that 'arg' can be NULL here, so the NULL check
cannot be removed. I'll send a v2.

Thanks,
Thorsten