When we exec a new task we forget to flush the set of locked GCS mode bits.
Since we do flush the rest of the state this means that if GCS is locked
the new task will be unable to enable GCS, it will be locked as being
disabled. Add the expected flush.

Fixes: fc84bc5378a8 ("arm64/gcs: Context switch GCS state for EL0")
Reported-by: Yury Khrustalev <Yury.Khrustalev@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index fba7ca102a8c..489554931231 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -292,6 +292,7 @@ static void flush_gcs(void)
 	current->thread.gcs_base = 0;
 	current->thread.gcs_size = 0;
 	current->thread.gcs_el0_mode = 0;
+	current->thread.gcs_el0_locked = 0;
 	write_sysreg_s(GCSCRE0_EL1_nTR, SYS_GCSCRE0_EL1);
 	write_sysreg_s(0, SYS_GCSPR_EL0);
 }

---
base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
change-id: 20251128-arm64-gcs-flush-lock-163eab9c22f4

Best regards,
--  
Mark Brown <broonie@kernel.org>

On Sat, Nov 29, 2025 at 12:48:45AM +0000, Mark Brown wrote:
> When we exec a new task we forget to flush the set of locked GCS mode bits.
> Since we do flush the rest of the state this means that if GCS is locked
> the new task will be unable to enable GCS, it will be locked as being
> disabled. Add the expected flush.
> 
> Fixes: fc84bc5378a8 ("arm64/gcs: Context switch GCS state for EL0")
> Reported-by: Yury Khrustalev <Yury.Khrustalev@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>

Thanks! I've tested this patch and it works as expected.

Tested-by: Yury Khrustalev <yury.khrustalev@arm.com>

> ---
>  arch/arm64/kernel/process.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index fba7ca102a8c..489554931231 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -292,6 +292,7 @@ static void flush_gcs(void)
>  	current->thread.gcs_base = 0;
>  	current->thread.gcs_size = 0;
>  	current->thread.gcs_el0_mode = 0;
> +	current->thread.gcs_el0_locked = 0;
>  	write_sysreg_s(GCSCRE0_EL1_nTR, SYS_GCSCRE0_EL1);
>  	write_sysreg_s(0, SYS_GCSPR_EL0);
>  }
> 
> ---
> base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
> change-id: 20251128-arm64-gcs-flush-lock-163eab9c22f4
> 
> Best regards,
> --  
> Mark Brown <broonie@kernel.org>
>