Re: [PATCH v2 bpf-next] arm64: mm: Complete the PTE store in ptep_try_set()

[Catalin Marinas <catalin.marinas@arm.com>]

On Sun, Jun 07, 2026 at 09:25:47PM -1000, Tejun Heo wrote:
> ptep_try_set() installs a kernel PTE with try_cmpxchg() but, unlike
> __set_pte(), skips the barriers that arm64 requires after writing a valid
> kernel PTE. Without them a subsequent access can fault instead of seeing
> the new mapping.
> 
> Issue them with emit_pte_barriers() rather than __set_pte_complete().
> ptep_try_set() must finish the store before it returns, but
> __set_pte_complete() would defer the barriers when the calling context is in
> lazy MMU mode.
> 
> v2: Emit the barriers directly instead of __set_pte_complete(). (Catalin)

Nit: I'd place this after the --- line.

> Fixes: 258df8fce42f ("mm: Add ptep_try_set() for lockless empty-slot installs")
> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> Link: https://lore.kernel.org/all/aiRFcz78QTZdIHHB@arm.com/
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
>  arch/arm64/include/asm/pgtable.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 3ce0f2a6cab6..3e579c26b383 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1838,7 +1838,16 @@ static inline bool ptep_try_set(pte_t *ptep, pte_t new_pte)
>  {
>  	pteval_t old = 0;
>  
> -	return try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte));
> +	if (!try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte)))
> +		return false;
> +
> +	/*
> +	 * The store must be complete by the time this returns, but the caller
> +	 * may be in lazy MMU mode, where __set_pte_complete() would defer the
> +	 * barriers. Issue them directly.
> +	 */
> +	emit_pte_barriers();
> +	return true;
>  }
>  #define ptep_try_set ptep_try_set

It looks fine now. Thanks!

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>