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

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Date:   Wed, 24 Jul 2019 16:37:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Price <steven.price@....com>
cc:     Mark Rutland <mark.rutland@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>, x86@...nel.org,
        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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.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, 24 Jul 2019, Steven Price wrote:
> On 24/07/2019 14:57, Thomas Gleixner wrote:
> > From your 14/N changelog:
> > 
> >> This keeps the output shorter and will help with a future change
> > 
> > I don't care about shorter at all. It's debug information.
> 
> Sorry, the "shorter" part was because Dave Hansen originally said[1]:
> > I think I'd actually be OK with the holes just not showing up.  I
> > actually find it kinda hard to read sometimes with the holes in there.
> > I'd be curious what others think though.

I missed that otherwise I'd have disagreed right away.

> > I really do not understand why you think that WE no longer care about the
> > level (and the size) of the holes. I assume that WE is pluralis majestatis
> > and not meant to reflect the opinion of you and everyone else.
> 
> Again, I apologise - that was sloppy wording in the commit message. By
> "we" I meant the code not any particular person.

Nothing to apologize. Common mistake of trying to impersonate code. That
always reads wrong :)

> > I have no idea whether you ever had to do serious work with PT dump, but I
> > surely have at various occasions including the PTI mess and I definitely
> > found the size and the level information from holes very useful.
> 
> On arm64 we don't have those lines, but equally it's possible they might
> be useful in the future. So this might be something to add.
> 
> As I said in a previous email[3] I was dropping the lines from the
> output assuming nobody had any objections. Since you find these lines
> useful, I'll see about reworking the change to retain the lines.

That would be great and as I saw in the other mail, Mark wants to have them
as well :)

That reminds me, that I had a patch when dealing with L1TF which printed
the PFNs so I could verify that the mitigations do what they are supposed
to do, but that patch got obviously lost somewhere down the road.

Thanks,

	tglx