From: Steven Price <steven.price@arm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
Mike Rapoport <rppt@linux.ibm.com>
Cc: "Mark Rutland" <Mark.Rutland@arm.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Catalin Marinas" <catalin.marinas@arm.com>,
x86@kernel.org, "Will Deacon" <will.deacon@arm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Andy Lutomirski" <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"James Morse" <james.morse@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org, "Liang,
Kan" <kan.liang@linux.intel.com>
Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros
Date: Fri, 1 Mar 2019 13:39:30 +0000 [thread overview]
Message-ID: <b8bd0f99-1c5e-7cf5-32dd-ab52d921e86c@arm.com> (raw)
In-Reply-To: <20190301123031.rw3dswcoaa2x7haq@kshutemo-mobl1>
On 01/03/2019 12:30, Kirill A. Shutemov wrote:
> On Fri, Mar 01, 2019 at 01:53:01PM +0200, Mike Rapoport wrote:
>> Him Kirill,
>>
>> On Fri, Feb 22, 2019 at 12:06:18AM +0300, Kirill A. Shutemov wrote:
>>> On Thu, Feb 21, 2019 at 05:16:46PM +0000, Steven Price wrote:
>>>>>> Note that in terms of the new page walking code, these new defines are
>>>>>> only used when walking a page table without a VMA (which isn't currently
>>>>>> done), so architectures which don't use p?d_large currently will work
>>>>>> fine with the generic versions. They only need to provide meaningful
>>>>>> definitions when switching to use the walk-without-a-VMA functionality.
>>>>>
>>>>> How other architectures would know that they need to provide the helpers
>>>>> to get walk-without-a-VMA functionality? This looks very fragile to me.
>>>>
>>>> Yes, you've got a good point there. This would apply to the p?d_large
>>>> macros as well - any arch which (inadvertently) uses the generic version
>>>> is likely to be fragile/broken.
>>>>
>>>> I think probably the best option here is to scrap the generic versions
>>>> altogether and simply introduce a ARCH_HAS_PXD_LARGE config option which
>>>> would enable the new functionality to those arches that opt-in. Do you
>>>> think this would be less fragile?
>>>
>>> These helpers are useful beyond pagewalker.
>>>
>>> Can we actually do some grinding and make *all* archs to provide correct
>>> helpers? Yes, it's tedious, but not that bad.
>>
>> Many architectures simply cannot support non-leaf entries at the higher
>> levels. I think letting the use a generic helper actually does make sense.
>
> I disagree.
>
> It's makes sense if the level doesn't exists on the arch.
This is what patch 24 [1] of the series does - if the level doesn't
exist then appropriate stubs are provided.
> But if the level exists, it will be less frugile to ask the arch to
> provide the helper. Even if it is dummy always-false.
The problem (as I see it), is we need a reliable set of p?d_large()
implementations to be able to walk arbitrary page tables. Either the
entire functionality of walking page tables without a VMA has to be an
opt-in per architecture, or we need to mandate that every architecture
provide these implementations.
I could provide an asm-generic header to provide a complete set of dummy
implementations for architectures that don't support large pages at all,
but that seems a bit overkill when most architectures only need to
define 2 or 3 implementations (the rest being provided by the
folded-levels automatically).
Thanks,
Steve
[1]
https://lore.kernel.org/lkml/20190227170608.27963-25-steven.price@arm.com/
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next prev parent reply other threads:[~2019-03-01 13:39 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 11:34 [PATCH v2 00/13] Convert x86 & arm64 to use generic page walk Steven Price
2019-02-21 11:34 ` [PATCH v2 01/13] arm64: mm: Add p?d_large() definitions Steven Price
2019-02-21 13:52 ` Mark Rutland
2019-02-21 11:34 ` [PATCH v2 02/13] x86/mm: " Steven Price
2019-02-21 14:21 ` Kirill A. Shutemov
2019-02-21 11:34 ` [PATCH v2 03/13] mm: Add generic p?d_large() macros Steven Price
2019-02-21 13:41 ` Mark Rutland
2019-02-21 14:28 ` Kirill A. Shutemov
2019-02-21 14:46 ` Steven Price
2019-02-21 14:57 ` Kirill A. Shutemov
2019-02-21 17:16 ` Steven Price
2019-02-21 21:06 ` Kirill A. Shutemov
2019-02-22 10:21 ` Steven Price
2019-03-01 11:53 ` Mike Rapoport
2019-03-01 12:30 ` Kirill A. Shutemov
2019-03-01 13:39 ` Steven Price [this message]
2019-03-03 7:12 ` Mike Rapoport
2019-03-04 14:35 ` Steven Price
2019-03-04 14:53 ` Mike Rapoport
2019-03-01 11:49 ` Mike Rapoport
2019-03-01 12:28 ` Kirill A. Shutemov
2019-02-21 11:34 ` [PATCH v2 04/13] mm: pagewalk: Add p4d_entry() and pgd_entry() Steven Price
2019-02-21 11:34 ` [PATCH v2 05/13] mm: pagewalk: Allow walking without vma Steven Price
2019-02-21 11:34 ` [PATCH v2 06/13] mm: pagewalk: Add 'depth' parameter to pte_hole Steven Price
2019-02-21 11:34 ` [PATCH v2 07/13] mm: pagewalk: Add test_p?d callbacks Steven Price
2019-02-21 11:34 ` [PATCH v2 08/13] arm64: mm: Convert mm/dump.c to use walk_page_range() Steven Price
2019-02-21 11:34 ` [PATCH v2 09/13] x86/mm: Point to struct seq_file from struct pg_state Steven Price
2019-02-21 11:34 ` [PATCH v2 10/13] x86/mm+efi: Convert ptdump_walk_pgd_level() to take a mm_struct Steven Price
2019-02-21 11:35 ` [PATCH v2 11/13] x86/mm: Convert ptdump_walk_pgd_level_debugfs() to take an mm_struct Steven Price
2019-02-21 11:35 ` [PATCH v2 12/13] x86/mm: Convert ptdump_walk_pgd_level_core() " Steven Price
2019-02-21 11:35 ` [PATCH v2 13/13] x86: mm: Convert dump_pagetables to use walk_page_range Steven Price
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