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

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Message-ID: <55bb026c-5d54-6ebf-608f-3f376fbec4e5@intel.com>
Date:   Wed, 28 Aug 2019 08:46:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     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 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.