linux-kernel - Re: [PATCH] mm/page_table_check: fix accessing unmapped ptep

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Message-ID: <CA+CK2bBJ3baj2Qt+9Wy1r==_Uym_UZJ+S-HRwFAsspPamctk_Q@mail.gmail.com>
Date:   Thu, 26 May 2022 14:31:06 -0400
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/page_table_check: fix accessing unmapped ptep

> > Miaohe, please store the ptep, or maybe drop this patch entirely.
>
> I think it's best to fix it.  I rewrote the changelog as
>
> : ptep is unmapped too early, so ptep could theoretically be accessed while
> : it's unmapped.  This might become a problem if/when CONFIG_HIGHPTE becomes
> : available on riscv.
> :
> : Fix it by deferring pte_unmap() until page table checking is done.
>
> I'll retain the Fixes:.  This doesn't imply cc:stable in MM, and anyone
> who backports the original patchset will want to know about this fixup.
Makes sense.


> And I queued a fixup for the thing Matthew noticed.
Thank you Andrew.

Pasha