linux-kernel - Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone

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Date:   Wed, 28 Aug 2019 17:51:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Song Liu <songliubraving@...com>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in
 pti_clone_pagetable()

On Wed, 28 Aug 2019, Dave Hansen wrote:
> On 8/28/19 7:24 AM, Thomas Gleixner wrote:
> > From: Song Liu <songliubraving@...com>
> > 
> > pti_clone_pmds() assumes that the supplied address is either:
> > 
> >  - properly PUD/PMD aligned
> > or
> >  - the address is actually mapped which means that independent
> >    of the mapping level (PUD/PMD/PTE) the next higher mapping
> >    exist.
> > 
> > If that's not the case the unaligned address can be incremented by PUD or
> > PMD size wrongly. All callers supply mapped and/or aligned addresses, but
> > for robustness sake, it's better to handle that case proper and to emit a
> > warning.
> 
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Song, did you ever root-cause the performance regression?  I thought
> there were still some mysteries there.

See Peter's series to rework the ftrace code patching ...