linux-kernel - Re: [PATCH v2 3/3] x86/pti/64: Remove the SYSCALL64 entry trampoline

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Date:   Fri, 7 Sep 2018 11:35:57 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Joerg Roedel <joro@...tes.org>, Jiri Olsa <jolsa@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 3/3] x86/pti/64: Remove the SYSCALL64 entry trampoline

On Mon, Sep 03, 2018 at 03:59:44PM -0700, Andy Lutomirski wrote:
> The SYSCALL64 trampoline has a couple of nice properties:
> 
>  - The usual sequence of SWAPGS followed by two GS-relative accesses to
>    set up RSP is somewhat slow because the GS-relative accesses need
>    to wait for SWAPGS to finish.  The trampoline approach allows
>    RIP-relative accesses to set up RSP, which avoids the stall.

...

> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> index 31341ae7309f..7e79154846c8 100644
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -434,11 +434,42 @@ static void __init pti_clone_p4d(unsigned long addr)
>  }
>  
>  /*
> - * Clone the CPU_ENTRY_AREA into the user space visible page table.
> + * Clone the CPU_ENTRY_AREA and associated data into the user space visible
> + * page table.
>   */
>  static void __init pti_clone_user_shared(void)
>  {
> +	unsigned cpu;

Make that

	unsigned int cpu;

Otherwise, patches removing complex code are always good!

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.