linux-kernel - Re: [PATCH v9 00/21] Generic page walk and ptdump

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Message-ID: <20190723101639.GD8085@lakrids.cambridge.arm.com>
Date:   Tue, 23 Jul 2019 11:16:40 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Steven Price <steven.price@....com>
Cc:     linux-mm@...ck.org, Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v9 00/21] Generic page walk and ptdump

On Mon, Jul 22, 2019 at 04:41:49PM +0100, Steven Price wrote:
> This is a slight reworking and extension of my previous patch set
> (Convert x86 & arm64 to use generic page walk), but I've continued the
> version numbering as most of the changes are the same. In particular
> this series ends with a generic PTDUMP implemention for arm64 and x86.
> 
> Many architectures current have a debugfs file for dumping the kernel
> page tables. Currently each architecture has to implement custom
> functions for this because the details of walking the page tables used
> by the kernel are different between architectures.
> 
> This series extends the capabilities of walk_page_range() so that it can
> deal with the page tables of the kernel (which have no VMAs and can
> contain larger huge pages than exist for user space). A generic PTDUMP
> implementation is the implemented making use of the new functionality of
> walk_page_range() and finally arm64 and x86 are switch to using it,
> removing the custom table walkers.
> 
> To enable a generic page table walker to walk the unusual mappings of
> the kernel we need to implement a set of functions which let us know
> when the walker has reached the leaf entry. After a suggestion from Will
> Deacon I've chosen the name p?d_leaf() as this (hopefully) describes
> the purpose (and is a new name so has no historic baggage). Some
> architectures have p?d_large macros but this is easily confused with
> "large pages".
> 
> Mostly this is a clean up and there should be very little functional
> change. The exceptions are:
> 
> * x86 PTDUMP debugfs output no longer display pages which aren't
>   present (patch 14).
> 
> * arm64 has the ability to efficiently process KASAN pages (which
>   previously only x86 implemented). This means that the combination of
>   KASAN and DEBUG_WX is now useable.

Are there any visible changes to the arm64 output?

Could you dump a before/after example somewhere?

Thanks,
Mark.