linux-kernel - Re: [PATCH 7/7] mm: Set pt

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Date:   Wed, 29 Apr 2020 03:52:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH 7/7] mm: Set pt_mm in PMD constructor

On Tue, Apr 28, 2020 at 12:44:49PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> By setting pt_mm for pages in use as page tables, we can help with
> debugging and lay the foundation for handling hardware errors in page
> tables more gracefully.  It also opens up the possibility for adding
> more sanity checks in the future.
> 
> Also set and clear the PageTable bit so that we know these are page tables.

As far as I can see you don't yet introduce any checks. It makes patchset
somewhat pointless.

I'm not entirely sure how such checks would look like. The single page
table tree would have at least two pt_mm: the owner and init_mm. Hugetlb
shared page tables would make a mess here. Hm?

-- 
 Kirill A. Shutemov