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From: Ingo Molnar <mingo@kernel.org>
To: Mateusz Guzik <mjguzik@gmail.com>
Cc: mingo@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Uros Bizjak <ubizjak@gmail.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86: predict __access_ok() returning true
Date: Tue, 1 Apr 2025 22:43:47 +0200	[thread overview]
Message-ID: <Z-xQAyPxQGvlg_hd@gmail.com> (raw)
In-Reply-To: <Z-xOFuT9Sl6VuFYi@gmail.com>


* Ingo Molnar <mingo@kernel.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

  reply	other threads:[~2025-04-01 20:43 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-01 20:30 [PATCH] x86: predict __access_ok() returning true Mateusz Guzik
2025-04-01 20:35 ` Ingo Molnar
2025-04-01 20:43   ` Ingo Molnar [this message]
2025-04-01 20:49     ` Mateusz Guzik
2025-04-01 21:00       ` Ingo Molnar
2025-04-01 21:11         ` Mateusz Guzik
2025-04-02  7:15   ` Uros Bizjak
2025-04-09 21:32 ` [tip: x86/asm] x86/uaccess: Predict valid_user_address() " tip-bot2 for Mateusz Guzik

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