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

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Date:   Tue, 28 Apr 2020 18:51:26 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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 0/7] Record the mm_struct in the page table pages

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

> 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.