linux-kernel - Re: [PATCH v2 3/4] mm: page table check

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Date:   Tue, 7 Dec 2021 16:05:08 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, rientjes@...gle.com, pjt@...gle.com,
        weixugc@...gle.com, gthelen@...gle.com, mingo@...hat.com,
        corbet@....net, will@...nel.org, rppt@...nel.org,
        keescook@...omium.org, tglx@...utronix.de, peterz@...radead.org,
        masahiroy@...nel.org, samitolvanen@...gle.com,
        dave.hansen@...ux.intel.com, x86@...nel.org, frederic@...nel.org,
        hpa@...or.com, aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com
Subject: Re: [PATCH v2 3/4] mm: page table check

On Sat,  4 Dec 2021 18:23:13 +0000 Pasha Tatashin <pasha.tatashin@...een.com> wrote:

> Check user page table entries at the time they are added and removed.
> 
> Allows to synchronously catch memory corruption issues related to double
> mapping.
> 
> When a pte for an anonymous page is added into page table, we verify that
> this pte does not already point to a file backed page, and vice versa if
> this is a file backed page that is being added we verify that this page
> does not have an anonymous mapping
> 
> We also enforce that read-only sharing for anonymous pages is allowed
> (i.e.  cow after fork).  All other sharing must be for file pages.
> 
> Page table check allows to protect and debug cases where "struct page"
> metadata became corrupted for some reason.  For example, when refcnt or
> mapcount become invalid.
> 
> ...
>
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1307,6 +1307,9 @@ config HAVE_ARCH_PFN_VALID
>  config ARCH_SUPPORTS_DEBUG_PAGEALLOC
>  	bool
>  
> +config ARCH_SUPPORTS_PAGE_TABLE_CHECK
> +	bool
> +

I guess a dependency on CONFIG_DEBUG_VM would be appropriate?