linux-kernel - Re: [PATCH 0/7] Record the mm_struct in the page table pages

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Message-ID: <20200524074230.GM1118872@kernel.org>
Date:   Sun, 24 May 2020 10:42:30 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>, 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 0/7] Record the mm_struct in the page table pages

On Tue, Apr 28, 2020 at 06:51:26PM -0700, Matthew Wilcox wrote:
> On Wed, Apr 29, 2020 at 03:26:24AM +0300, Kirill A. Shutemov wrote:
> > On Tue, Apr 28, 2020 at 12:44:42PM -0700, Matthew Wilcox wrote:
> > > From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > > 
> > > Pages which are in use as page tables have some space unused in struct
> > > page.  It would be handy to have a pointer to the struct mm_struct that
> > > they belong to so that we can handle uncorrectable errors in page tables
> > > more gracefully.  There are a few other things we could use it for too,
> > > such as checking that the page table entry actually belongs to the task
> > > we think it ought to.  This patch series does none of that, but does
> > > lay the groundwork for it.
> > > 
> > > Matthew Wilcox (Oracle) (7):
> > 
> > How does it work for kernel side of virtual address space?
> 
> init_mm

A note to keep in mind is that most of the kernel page tables are seen
as PG_reserved rather than PageTable().

> > And your employer may be interested in semantics around
> > CONFIG_ARCH_WANT_HUGE_PMD_SHARE :P
> 
> I was thinking about that.  Right now, it's only useful for debugging
> purposes (as you point out in a later email).  I think it's OK if shared
> PMDs aren't supported as well as regular PTEs, just because there are
> so few of them that uncorrectable errors are less likely to strike in
> those pages.
> 

-- 
Sincerely yours,
Mike.