linux-kernel - Re: [patch 0/2] x86/mm/pti: Robustness updates

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Message-ID: <20190828160342.GF17205@worktop.programming.kicks-ass.net>
Date:   Wed, 28 Aug 2019 18:03:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Song Liu <songliubraving@...com>,
        Joerg Roedel <jroedel@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [patch 0/2] x86/mm/pti: Robustness updates

On Wed, Aug 28, 2019 at 04:24:45PM +0200, Thomas Gleixner wrote:
> Following up on the discussions around the patch Song submitted to 'cure' a
> iTLB related performance regression, I picked up Song's patch which makes
> clone_page_tables() more robust by handling unaligned addresses proper and
> added one which prevents calling into the PTI code when PTI is enabled
> compile time, but disabled at runtime (command line or CPU not affected).
> 
> There is no point in calling into those PTI functions unconditionally. The
> resulting page tables are the same before and after the change which makes
> sense as the code clones the kernel page table into the secondary page
> table space which is available but not used when PTI is boot time disabled.
> 
> But even if it does not do damage today, this could have nasty side effect
> when the PTI code is changed, extended etc. later.
> 

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>