linux-kernel - Re: [PATCH v2 2/3] x86/entry/64: Use the TSS sp2 slot for SYSCALL/SYSRET scratch space

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Date:   Fri, 7 Sep 2018 10:00:41 +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 2/3] x86/entry/64: Use the TSS sp2 slot for
 SYSCALL/SYSRET scratch space

On Mon, Sep 03, 2018 at 03:59:43PM -0700, Andy Lutomirski wrote:
> In the non-trampoline SYSCALL64 path, we use a percpu variable to
> temporarily store the user RSP value.  Instead of a separate
> variable, use the otherwise unused sp2 slot in the TSS.  This will
> improve cache locality, as the sp1 slot is already used in the same
> code to find the kernel stack.  It will also simplify a future
> change to make the non-trampoline path work in PTI mode.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_64.S        | 16 +++++++++-------
>  arch/x86/include/asm/processor.h |  6 ++++++
>  arch/x86/kernel/asm-offsets.c    |  3 ++-
>  arch/x86/kernel/process_64.c     |  2 --
>  arch/x86/xen/xen-asm_64.S        |  8 +++++---
>  5 files changed, 22 insertions(+), 13 deletions(-)

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

-- 
Regards/Gruss,
    Boris.

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