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

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Date:   Wed, 24 Jul 2019 15:07:35 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Steven Price <steven.price@....com>, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        James Morse <james.morse@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH v9 00/21] Generic page walk and ptdump

On Wed, Jul 24, 2019 at 03:57:33PM +0200, Thomas Gleixner wrote:
> On Wed, 24 Jul 2019, Steven Price wrote:
> > On 23/07/2019 11:16, Mark Rutland wrote:
> > > Are there any visible changes to the arm64 output?
> > 
> > arm64 output shouldn't change. I've confirmed that "efi_page_tables" is
> > identical on a Juno before/after the change. "kernel_page_tables"
> > obviously will vary depending on the exact layout of memory, but the
> > format isn't changed.
> > 
> > x86 output does change due to patch 14. In this case the change is
> > removing the lines from the output of the form...
> > 
> > > 0xffffffff84800000-0xffffffffa0000000         440M                               pmd
> > 
> > ...which are unpopulated areas of the memory map. Populated lines which
> > have attributes are unchanged.
> 
> Having the hole size and the level in the dump is a very conveniant thing.

Mhmm; I thought that we logged which level was empty on arm64 (but
apparently not), since knowing the structure can be important.

> Right now we have:
> 
> 0xffffffffc0427000-0xffffffffc042b000          16K     ro                     NX pte
> 0xffffffffc042b000-0xffffffffc042e000          12K     RW                     NX pte
> 0xffffffffc042e000-0xffffffffc042f000           4K                               pte
> 0xffffffffc042f000-0xffffffffc0430000           4K     ro                     x  pte
> 0xffffffffc0430000-0xffffffffc0431000           4K     ro                     NX pte
> 0xffffffffc0431000-0xffffffffc0433000           8K     RW                     NX pte
> 0xffffffffc0433000-0xffffffffc0434000           4K                               pte
> 0xffffffffc0434000-0xffffffffc0436000           8K     ro                     x  pte
> 0xffffffffc0436000-0xffffffffc0438000           8K     ro                     NX pte
> 0xffffffffc0438000-0xffffffffc043a000           8K     RW                     NX pte
> 0xffffffffc043a000-0xffffffffc043f000          20K                               pte
> 0xffffffffc043f000-0xffffffffc0444000          20K     ro                     x  pte
> 0xffffffffc0444000-0xffffffffc0447000          12K     ro                     NX pte
> 0xffffffffc0447000-0xffffffffc0449000           8K     RW                     NX pte
> 0xffffffffc0449000-0xffffffffc044f000          24K                               pte
> 0xffffffffc044f000-0xffffffffc0450000           4K     ro                     x  pte
> 0xffffffffc0450000-0xffffffffc0451000           4K     ro                     NX pte
> 0xffffffffc0451000-0xffffffffc0453000           8K     RW                     NX pte
> 0xffffffffc0453000-0xffffffffc0458000          20K                               pte
> 0xffffffffc0458000-0xffffffffc0459000           4K     ro                     x  pte
> 0xffffffffc0459000-0xffffffffc045b000           8K     ro                     NX pte
> 
> with your change this becomes:
> 
> 0xffffffffc0427000-0xffffffffc042b000          16K     ro                     NX pte
> 0xffffffffc042b000-0xffffffffc042e000          12K     RW                     NX pte
> 0xffffffffc042f000-0xffffffffc0430000           4K     ro                     x  pte
> 0xffffffffc0430000-0xffffffffc0431000           4K     ro                     NX pte
> 0xffffffffc0431000-0xffffffffc0433000           8K     RW                     NX pte
> 0xffffffffc0434000-0xffffffffc0436000           8K     ro                     x  pte
> 0xffffffffc0436000-0xffffffffc0438000           8K     ro                     NX pte
> 0xffffffffc0438000-0xffffffffc043a000           8K     RW                     NX pte
> 0xffffffffc043f000-0xffffffffc0444000          20K     ro                     x  pte
> 0xffffffffc0444000-0xffffffffc0447000          12K     ro                     NX pte
> 0xffffffffc0447000-0xffffffffc0449000           8K     RW                     NX pte
> 0xffffffffc044f000-0xffffffffc0450000           4K     ro                     x  pte
> 0xffffffffc0450000-0xffffffffc0451000           4K     ro                     NX pte
> 0xffffffffc0451000-0xffffffffc0453000           8K     RW                     NX pte
> 0xffffffffc0458000-0xffffffffc0459000           4K     ro                     x  pte
> 0xffffffffc0459000-0xffffffffc045b000           8K     ro                     NX pte
> 
> which is 5 lines less, but a pain to figure out the size of the holes. And
> it becomes even more painful when the holes go across different mapping
> levels.

I agree.

Steven, could you align arm64 with the x86 behaviour here?

Thanks,
Mark.