From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Luck, Tony" <tony.luck@intel.com>
Date: Mon, 04 Mar 2019 19:06:37 +0000
Subject: Re: [PATCH v3 08/34] ia64: mm: Add p?d_large() definitions
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To: Steven Price <steven.price@arm.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, Mark Rutland <Mark.Rutland@arm.com>, linux-ia64@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Dave Hansen <dave.hansen@linux.intel.com>, Will Deacon <will.deacon@arm.com>, linux-mm@kvack.org, "H. Peter Anvin" <hpa@zytor.com>, "Liang, Kan" <kan.liang@linux.intel.com>, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, Fenghua Yu <fenghua.yu@intel.com>, Arnd Bergmann <arnd@arndb.de>, =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, linux-arm-kernel@lists.infradead.org, Ard Biesheuvel <ard.biesheuvel@linaro.org>, linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>

On Mon, Mar 04, 2019 at 01:16:47PM +0000, Steven Price wrote:
> 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.

ia64 has several ways to manage page tables. The one
used by Linux has multi-level table walks like other
architectures, but we don't allow mixing of different
page sizes within a "region" (there are eight regions
selected by the high 3 bits of the virtual address).

Is the series in some GIT tree that I can pull, rather
than tracking down all 34 pieces?  I can try it out and
see if things work/break.

-Tony