linux-kernel - Re: [PATCH v3 08/34] ia64: mm: Add p?d

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Message-ID: <15100043-26e4-2ee1-28fe-101e12f74926@arm.com>
Date:   Mon, 4 Mar 2019 13:16:47 +0000
From:   Steven Price <steven.price@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Mark Rutland <Mark.Rutland@....com>, linux-ia64@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Will Deacon <will.deacon@....com>, linux-mm@...ck.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Tony Luck <tony.luck@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, James Morse <james.morse@....com>
Subject: Re: [PATCH v3 08/34] ia64: mm: Add p?d_large() definitions

On 01/03/2019 21:57, Kirill A. Shutemov wrote:
> On Wed, Feb 27, 2019 at 05:05:42PM +0000, Steven Price wrote:
>> walk_page_range() is going to be allowed to walk page tables other than
>> those of user space. For this it needs to know when it has reached a
>> 'leaf' entry in the page tables. This information is provided by the
>> p?d_large() functions/macros.
>>
>> For ia64 leaf entries are always at the lowest level, so implement
>> stubs returning 0.
> 
> Are you sure about this? I see pte_mkhuge defined for ia64 and Kconfig
> contains hugetlb references.
> 

I'm not completely familiar with ia64, but my understanding is that it
doesn't have the situation where a page table walk ends early - there is
always the full depth of entries. The p?d_huge() functions always return 0.

However my understanding is that it does support huge TLB entries, so
when populating the TLB a region larger than a standard page can be mapped.

I'd definitely welcome review by someone more familiar with ia64 to
check my assumptions.

Thanks,

Steve