linux-kernel - Re: [PATCH] x86: predict __access

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Message-ID: <Z-xQAyPxQGvlg_hd@gmail.com>
Date: Tue, 1 Apr 2025 22:43:47 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Uros Bizjak <ubizjak@...il.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: predict __access_ok() returning true


* Ingo Molnar <mingo@...nel.org> wrote:

> It's also the right place to have the hint: that user addresses are 
> valid is the common case we optimize for.
> 
> Thanks,
> 
> 	Ingo
> 
>  arch/x86/include/asm/uaccess_64.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
> index c52f0133425b..4c13883371aa 100644
> --- a/arch/x86/include/asm/uaccess_64.h
> +++ b/arch/x86/include/asm/uaccess_64.h
> @@ -54,7 +54,7 @@ static inline unsigned long __untagged_addr_remote(struct mm_struct *mm,
>  #endif
>  
>  #define valid_user_address(x) \
> -	((__force unsigned long)(x) <= runtime_const_ptr(USER_PTR_MAX))
> +	likely((__force unsigned long)(x) <= runtime_const_ptr(USER_PTR_MAX))

Should we go this way, this is the safe macro variant:

   #define valid_user_address(x) \
	(likely((__force unsigned long)(x) <= runtime_const_ptr(USER_PTR_MAX)))

But this compiler bug sounds weird ...

Thanks,

	Ingo