Re: [PATCH 1/7] arm64: uaccess: Add batched kernel nofault accessors

[bot+bpf-ci]

> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 9f5bd9c69c24..1a14eb2a51dc 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -270,28 +270,43 @@ do {									\
>  #define get_user	__get_user
>
>  /*
> - * We must not call into the scheduler between __mte_enable_tco_async() and
> - * __mte_disable_tco_async(). As `dst` and `src` may contain blocking
> - * functions, we must evaluate these outside of the critical section.
> + * Nofault load without TCO management for use inside a
> + * __begin/__end_kernel_nofault_bare() region.
>   */
> -#define __get_kernel_nofault(dst, src, type, err_label)			\
> +#define __get_kernel_nofault_bare(dst, src, type, err_label)		\
>  do {									\
>  	__typeof__(dst) __gkn_dst = (dst);				\
>  	__typeof__(src) __gkn_src = (src);				\
>  	do { 								\
>  		__label__ __gkn_label;					\
> -									\
> -		__mte_enable_tco_async();				\
>  		__raw_get_mem("ldr", *((type *)(__gkn_dst)),		\
>  		      (__force type *)(__gkn_src), __gkn_label, K);	\
> -		__mte_disable_tco_async();				\
>  		break;							\
>  	__gkn_label:							\
> -		__mte_disable_tco_async();				\
>  		goto err_label;						\
>  	} while (0);							\
>  } while (0)
>
>  /*
> + * We must not call into the scheduler between __mte_enable_tco_async() and
> + * __mte_disable_tco_async(). As dst and src may contain blocking functions,
> + * evaluate them before overriding TCO.
> + */
> +#define __get_kernel_nofault(dst, src, type, err_label)			\
> +do {									\
> +	__label__ __gkn_tco_err;					\
> +	__typeof__(dst) __gkn_tco_dst = (dst);				\
> +	__typeof__(src) __gkn_tco_src = (src);				\
> +	__mte_enable_tco_async();					\
> +	__get_kernel_nofault_bare(__gkn_tco_dst, __gkn_tco_src, type,	\
> +				     __gkn_tco_err);			\
> +	__mte_disable_tco_async();					\
> +	break;								\
> +__gkn_tco_err:								\
> +	__mte_disable_tco_async();					\
> +	goto err_label;							\
> +} while (0)

This isn't a bug, but the get and put variants now carry the same rule
in two different wordings - would it read better to keep the two
comments identical, or to have the put side just point at the get side?

The comment above __get_kernel_nofault says "As dst and src may contain
blocking functions, evaluate them before overriding TCO," while the
comment above __put_kernel_nofault keeps the original "As `dst` and
`src` may contain blocking functions, we must evaluate these outside of
the critical section" - including the backticks that the get variant
dropped.

Also, should the wrapped argument line up under the open paren here
(four tabs plus two spaces rather than five)?

> +	__get_kernel_nofault_bare(__gkn_tco_dst, __gkn_tco_src, type,	\
> +				     __gkn_tco_err);			\

The continuation line sits at column 37, while the open parenthesis of
__get_kernel_nofault_bare( sits at column 34. The same three-column
offset appears in __put_kernel_nofault at line 412.

[ ... ]

> @@ -366,28 +381,48 @@ do {									\
>
>  #define put_user	__put_user
>
> -/*
> - * We must not call into the scheduler between __mte_enable_tco_async() and
> - * __mte_disable_tco_async(). As `dst` and `src` may contain blocking
> - * functions, we must evaluate these outside of the critical section.
> - */
> -#define __put_kernel_nofault(dst, src, type, err_label)			\
> +/* Nofault store without TCO management; see __get_kernel_nofault_bare. */
> +#define __put_kernel_nofault_bare(dst, src, type, err_label)		\
>  do {									\
>  	__typeof__(dst) __pkn_dst = (dst);				\
>  	__typeof__(src) __pkn_src = (src);				\
>  									\
>  	do {								\
>  		__label__ __pkn_err;					\
> -		__mte_enable_tco_async();				\
>  		__raw_put_mem("str", *((type *)(__pkn_src)),		\
>  			      (__force type *)(__pkn_dst), __pkn_err, K);	\
> -		__mte_disable_tco_async();				\
>  		break;							\
>  	__pkn_err:							\
> -		__mte_disable_tco_async();				\
>  		goto err_label;						\
>  	} while (0);							\
> -} while(0)
> +} while (0)
> +
> +/*
> + * We must not call into the scheduler between __mte_enable_tco_async() and
> + * __mte_disable_tco_async(). As `dst` and `src` may contain blocking
> + * functions, we must evaluate these outside of the critical section.
> + */

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/32751368606