[PATCH 2/2] arm64/mm: avoid max_pinned_asids underflow

[Will Deacon]

On Thu, Feb 19, 2026 at 12:30:07PM +0000, Reda CHERKAOUI wrote:
> Signed-off-by: Reda CHERKAOUI <redacherkaoui67 at gmail.com>

Please add a commit message.

>  arch/arm64/mm/context.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index 74c1ece7db78..fdcee1127954 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -386,11 +386,7 @@ static int asids_update_limit(void)
>  		if (pinned_asid_map)
>  			set_kpti_asid_bits(pinned_asid_map);
>  	}
> -	/*
> -	 * Expect allocation after rollover to fail if we don't have at least
> -	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
> -	 */

Why remove this comment?

> -	WARN_ON(num_available_asids - 1 <= num_possible_cpus());
> +
>  	pr_info("ASID allocator initialised with %lu entries\n",
>  		num_available_asids);
>  
> @@ -399,7 +395,11 @@ static int asids_update_limit(void)
>  	 * even if all CPUs have a reserved ASID and the maximum number of ASIDs
>  	 * are pinned, there still is at least one empty slot in the ASID map.
>  	 */
> -	max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
> +	if (WARN_ON(num_available_asids <= num_possible_cpus() + 2))
> +		max_pinned_asids = 0;
> +	else
> +		max_pinned_asids = num_available_asids - num_possible_cpus() - 2;

How about something like the below instead?

Will

--->8

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index b2ac06246327..94cffda52e4c 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -380,20 +380,23 @@ static int asids_update_limit(void)
 		if (pinned_asid_map)
 			set_kpti_asid_bits(pinned_asid_map);
 	}
+
 	/*
 	 * Expect allocation after rollover to fail if we don't have at least
 	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
 	 */
-	WARN_ON(num_available_asids - 1 <= num_possible_cpus());
+	if (!WARN_ON(num_available_asids - 1 <= num_possible_cpus())) {
+		/*
+		 * There must always be an ASID available after rollover. Ensure
+		 * that, even if all CPUs have a reserved ASID and the maximum
+		 * number of ASIDs are pinned, there still is at least one empty
+		 * slot in the ASID map.
+		 */
+		max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
+	}
+
 	pr_info("ASID allocator initialised with %lu entries\n",
 		num_available_asids);
-
-	/*
-	 * There must always be an ASID available after rollover. Ensure that,
-	 * even if all CPUs have a reserved ASID and the maximum number of ASIDs
-	 * are pinned, there still is at least one empty slot in the ASID map.
-	 */
-	max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
 	return 0;
 }
 arch_initcall(asids_update_limit);