linux-kernel - Re: [PATCH v1 1/4] kasan: introduce set_pmd_early

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Date:   Wed, 15 Jan 2020 10:54:45 +0000
From:   Sergey Dyasli <sergey.dyasli@...rix.com>
To:     Juergen Gross <jgross@...e.com>
CC:     <xen-devel@...ts.xen.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        "Dmitry Vyukov" <dvyukov@...gle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        George Dunlap <george.dunlap@...rix.com>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "sergey.dyasli@...rix.com >> Sergey Dyasli" 
        <sergey.dyasli@...rix.com>
Subject: Re: [PATCH v1 1/4] kasan: introduce set_pmd_early_shadow()

Hi Juergen,

On 08/01/2020 15:20, Sergey Dyasli wrote:
> It is incorrect to call pmd_populate_kernel() multiple times for the
> same page table. Xen notices it during kasan_populate_early_shadow():
>
>     (XEN) mm.c:3222:d155v0 mfn 3704b already pinned
>
> This happens for kasan_early_shadow_pte when USE_SPLIT_PTE_PTLOCKS is
> enabled. Fix this by introducing set_pmd_early_shadow() which calls
> pmd_populate_kernel() only once and uses set_pmd() afterwards.
>
> Signed-off-by: Sergey Dyasli <sergey.dyasli@...rix.com>

Looks like the plan to use set_pmd() directly has failed: it's an
arch-specific function and can't be used in arch-independent code
(as kbuild test robot has proven).

Do you see any way out of this other than disabling SPLIT_PTE_PTLOCKS
for PV KASAN?

--
Thanks,
Sergey