linux-kernel - Re: [PATCH 01/13] arm64: mm: Add p?d

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Message-ID: <20190218170451.GB10145@lakrids.cambridge.arm.com>
Date:   Mon, 18 Feb 2019 17:04:51 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Steven Price <steven.price@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>, x86@...nel.org,
        Will Deacon <will.deacon@....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>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 01/13] arm64: mm: Add p?d_large() definitions

On Mon, Feb 18, 2019 at 03:30:38PM +0000, Steven Price wrote:
> On 18/02/2019 15:06, Peter Zijlstra wrote:
> > On Mon, Feb 18, 2019 at 02:29:52PM +0000, Mark Rutland wrote:
> >> I think that Peter means p?d_huge(x) should imply p?d_large(x), e.g.
> >>
> >> #define pmd_large(x) \
> >> 	(pmd_sect(x) || pmd_huge(x) || pmd_trans_huge(x))
> >>
> >> ... which should work regardless of CONFIG_HUGETLB_PAGE.
> > 
> > Yep, that.
> 
> I'm not aware of a situation where pmd_huge(x) is true but pmd_sect(x)
> isn't. Equally for pmd_huge(x) and pmd_trans_huge(x).
> 
> What am I missing?

Having dug for a bit, I think you're right in asserting that pmd_sect()
should cover those.

I had worried that wouldn't cater for contiguous pmd entries, but those
have to be contiguous section entries, so they get picked up.

That said, do we have any special handling for contiguous PTEs? We use
those in kernel mappings regardless of hugetlb support, and I didn't
spot a pte_large() helper.

Thanks,
Mark.