linux-kernel - Re: [PATCH] Documentation/page_tables: Add info about MMU/TLB and Page Faults

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Message-ID: <3770829.kQq0lBPeGt@suse>
Date:   Wed, 09 Aug 2023 15:00:31 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Jonathan Corbet <corbet@....net>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] Documentation/page_tables: Add info about MMU/TLB and Page Faults

On lunedì 7 agosto 2023 12:50:10 CEST Mike Rapoport wrote:
> Hi Fabio,
> 
> On Fri, Jul 28, 2023 at 01:53:01PM +0200, Fabio M. De Francesco wrote:
> > Extend page_tables.rst by adding a section about the role of MMU and TLB
> > in translating between virtual addresses and physical page frames.
> > Furthermore explain the concept behind Page Faults and how the Linux
> > kernel handles TLB misses. Finally briefly explain how and why to disable
> > the page faults handler.
> > 
> > [snip]
> >
> > +MMU, TLB, and Page Faults
> > +=========================
> > +
> > +The `Memory Management Unit (MMU)` is a hardware component that handles
> > virtual +to physical address translations. It may use relatively small
> > caches in hardware +called `Translation Lookaside Buffers (TLBs)` and 
`Page
> > Walk Caches` to speed up +these translations.
> > +
> > +When a process wants to access a memory location, the CPU provides a
> > virtual
> > +address to the MMU, which then uses the MMU to check access permissions 
and
> > +dirty bits, and if possible it resolves the physical address and consents
> > the +requested type of access to the corresponding physical address.
> 
> Essentially any access to a memory location involves the translation from
> virtual to physical, not only when processes access memory.

Mike,

I'm cutting everything from here on because I agree with your comments, so I 
could just write a long list of 'I agree', 'I understand' and the like. I want 
to avoid readers from the aforementioned list :-)

I think (actually, I hope) that I have understood everything correctly. I will 
send a new version with the necessary corrections by the end of this week.

Thanks again for your comments and suggestions.

Fabio