linux-kernel - Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until the first LAM user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y8adEg2CYUSVpwtk@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Jan 2023 14:05:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until
 the first LAM user

On Wed, Jan 11, 2023 at 03:37:27PM +0300, Kirill A. Shutemov wrote:

>  #define __untagged_addr(untag_mask, addr)	({			\
>  	u64 __addr = (__force u64)(addr);				\
> -	s64 sign = (s64)__addr >> 63;					\
> -	__addr &= untag_mask | sign;					\
> +	if (static_branch_likely(&tagged_addr_key)) {			\
> +		s64 sign = (s64)__addr >> 63;				\
> +		__addr &= untag_mask | sign;				\
> +	}								\
>  	(__force __typeof__(addr))__addr;				\
>  })
>  
> #define untagged_addr(addr) __untagged_addr(current_untag_mask(), addr)

Is the compiler clever enough to put the memop inside the branch?