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Date:   Wed, 28 Aug 2019 17:51:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Dave Hansen <dave.hansen@intel.com>
cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Song Liu <songliubraving@fb.com>,
        Joerg Roedel <jroedel@suse.de>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Rik van Riel <riel@surriel.com>
Subject: Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in
 pti_clone_pagetable()
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References: <20190828142445.454151604@linutronix.de> <20190828143123.971884723@linutronix.de> <55bb026c-5d54-6ebf-608f-3f376fbec4e5@intel.com>
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On Wed, 28 Aug 2019, Dave Hansen wrote:
> On 8/28/19 7:24 AM, Thomas Gleixner wrote:
> > From: Song Liu <songliubraving@fb.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@linux.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 ...