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From: Steven Price <steven.price@arm.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>,
	Mike Rapoport <rppt@linux.ibm.com>
Cc: "Mark Rutland" <Mark.Rutland@arm.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.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 Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Linux MM" <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-m68k <linux-m68k@lists.linux-m68k.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Liang, Kan" <kan.liang@linux.intel.com>
Subject: Re: [PATCH v3 09/34] m68k: mm: Add p?d_large() definitions
Date: Thu, 28 Feb 2019 12:04:08 +0000	[thread overview]
Message-ID: <a17f5ad7-9fba-9d51-4d6e-7a9effe81e4e@arm.com> (raw)
In-Reply-To: <CAMuHMdU5gn6ftAHNwHNPDoUy_JvcZLcXbkk1hvUmYxtfJRfTTQ@mail.gmail.com>

On 28/02/2019 11:53, Geert Uytterhoeven wrote:
> Hi Mike,
> 
> On Thu, Feb 28, 2019 at 12:37 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>> On Wed, Feb 27, 2019 at 08:27:40PM +0100, Geert Uytterhoeven wrote:
>>> On Wed, Feb 27, 2019 at 6:07 PM Steven Price <steven.price@arm.com> 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 m68k, we don't support large pages, so add stubs returning 0
>>>>
>>>> CC: Geert Uytterhoeven <geert@linux-m68k.org>
>>>> CC: linux-m68k@lists.linux-m68k.org
>>>> Signed-off-by: Steven Price <steven.price@arm.com>
>>>
>>> Thanks for your patch!
>>>
>>>>  arch/m68k/include/asm/mcf_pgtable.h      | 2 ++
>>>>  arch/m68k/include/asm/motorola_pgtable.h | 2 ++
>>>>  arch/m68k/include/asm/pgtable_no.h       | 1 +
>>>>  arch/m68k/include/asm/sun3_pgtable.h     | 2 ++
>>>>  4 files changed, 7 insertions(+)
>>>
>>> If the definitions are the same, why not add them to
>>> arch/m68k/include/asm/pgtable.h instead?

I don't really understand the structure of m68k, so I just followed the
existing layout (arch/m68k/include/asm/pgtable.h is basically empty). I
believe the following patch would be functionally equivalent.

----8<----
diff --git a/arch/m68k/include/asm/pgtable.h
b/arch/m68k/include/asm/pgtable.h
index ad15d655a9bf..6f6d463e69c1 100644
--- a/arch/m68k/include/asm/pgtable.h
+++ b/arch/m68k/include/asm/pgtable.h
@@ -3,4 +3,9 @@
 #include <asm/pgtable_no.h>
 #else
 #include <asm/pgtable_mm.h>
+
+#define pmd_large(pmd)		(0)
+
 #endif
+
+#define pgd_large(pgd)		(0)
----8<----

Let me know if you'd prefer that

>> Maybe I'm missing something, but why the stubs have to be defined in
>> arch/*/include/asm/pgtable.h rather than in include/asm-generic/pgtable.h?
> 
> That would even make more sense, given most architectures don't
> support huge pages.

Where the architecture has folded a level stubs are provided by the
asm-generic layer, see this later patch:

https://lore.kernel.org/lkml/20190227170608.27963-25-steven.price@arm.com/

However just because an architecture port doesn't (currently) support
huge pages doesn't mean that the architecture itself can't have large[1]
mappings at higher levels of the page table. For instance an
architecture might use large pages for the linear map but not support
huge page mappings for user space.

My previous posting of this series attempted to define generic versions
of p?d_large(), but it was pointed out to me that this was fragile and
having a way of knowing whether the page table was a 'leaf' is actually
useful, so I've attempted to implement for all architectures. See the
discussion here:
https://lore.kernel.org/lkml/20190221113502.54153-1-steven.price@arm.com/T/#mf0bd0155f185a19681b48a288be212ed1596e85d

Steve

[1] Note I've tried to use the term "large page" where I mean that page
table walk terminates early, and "huge page" for the Linux concept of
combining a large area of memory to reduce TLB pressure. Some
architectures have ways of mapping a large block in the TLB without
reducing the number of levels in the table walk - for example contiguous
hint bits in the page table entries.

  reply	other threads:[~2019-02-28 12:04 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-27 17:05 [PATCH v3 00/34] Convert x86 & arm64 to use generic page walk Steven Price
2019-02-27 17:05 ` [PATCH v3 01/34] alpha: mm: Add p?d_large() definitions Steven Price
2019-02-27 17:05 ` [PATCH v3 02/34] arc: " Steven Price
2019-02-27 18:18   ` Vineet Gupta
2019-02-27 17:05 ` [PATCH v3 03/34] arm: " Steven Price
2019-03-01 21:47   ` Kirill A. Shutemov
2019-03-04 11:56     ` Steven Price
2019-03-04 13:10       ` Kirill A. Shutemov
2019-02-27 17:05 ` [PATCH v3 04/34] arm64: " Steven Price
2019-02-27 17:05 ` [PATCH v3 05/34] c6x: " Steven Price
2019-03-01 21:48   ` Kirill A. Shutemov
2019-03-04 12:01     ` Steven Price
2019-03-04 13:11       ` Kirill A. Shutemov
2019-02-27 17:05 ` [PATCH v3 06/34] csky: " Steven Price
2019-03-01 21:51   ` Kirill A. Shutemov
2019-02-27 17:05 ` [PATCH v3 07/34] hexagon: " Steven Price
2019-02-27 17:05 ` [PATCH v3 08/34] ia64: " Steven Price
2019-03-01 21:57   ` Kirill A. Shutemov
2019-03-04 13:16     ` Steven Price
2019-03-04 19:06       ` Luck, Tony
2019-03-06 13:45         ` Steven Price
2019-02-27 17:05 ` [PATCH v3 09/34] m68k: " Steven Price
2019-02-27 19:27   ` Geert Uytterhoeven
2019-02-28 11:36     ` Mike Rapoport
2019-02-28 11:53       ` Geert Uytterhoeven
2019-02-28 12:04         ` Steven Price [this message]
2019-03-01 11:45           ` Mike Rapoport
2019-02-27 17:05 ` [PATCH v3 10/34] microblaze: " Steven Price
2019-02-27 17:05 ` [PATCH v3 11/34] mips: " Steven Price
2019-02-28  2:15   ` Paul Burton
2019-02-28 12:11     ` Steven Price
2019-02-28 18:55       ` Paul Burton
2019-03-01 11:02         ` Steven Price
2019-02-27 17:05 ` [PATCH v3 12/34] nds32: " Steven Price
2019-02-27 17:05 ` [PATCH v3 13/34] nios2: " Steven Price
2019-02-27 17:05 ` [PATCH v3 14/34] openrisc: " Steven Price
2019-02-27 17:05 ` [PATCH v3 15/34] parisc: " Steven Price
2019-02-27 18:54   ` Helge Deller
2019-03-01 22:12     ` Kirill A. Shutemov
2019-03-05 21:45       ` Helge Deller
2019-02-27 17:05 ` [PATCH v3 16/34] powerpc: " Steven Price
2019-02-27 17:05 ` [PATCH v3 17/34] riscv: " Steven Price
2019-02-27 17:05 ` [PATCH v3 18/34] s390: " Steven Price
2019-02-27 17:40   ` Martin Schwidefsky
2019-02-28 11:43     ` Steven Price
2019-02-27 17:05 ` [PATCH v3 19/34] sh: " Steven Price
2019-02-27 17:05 ` [PATCH v3 20/34] sparc: " Steven Price
2019-02-27 18:38   ` David Miller
2019-02-28 11:49     ` Steven Price
2019-02-27 17:05 ` [PATCH v3 21/34] um: " Steven Price
2019-02-27 17:05 ` [PATCH v3 22/34] unicore32: " Steven Price
2019-02-27 17:05 ` [PATCH v3 23/34] xtensa: " Steven Price
2019-02-27 17:29   ` Max Filippov
2019-02-27 17:05 ` [PATCH v3 24/34] mm: Add generic p?d_large() macros Steven Price
2019-02-27 17:05 ` [PATCH v3 25/34] mm: pagewalk: Add p4d_entry() and pgd_entry() Steven Price
2019-02-27 17:06 ` [PATCH v3 26/34] mm: pagewalk: Allow walking without vma Steven Price
2019-02-27 17:06 ` [PATCH v3 27/34] mm: pagewalk: Add 'depth' parameter to pte_hole Steven Price
2019-02-27 17:38   ` Dave Hansen
2019-02-28 11:28     ` Steven Price
2019-02-28 19:00       ` Dave Hansen
2019-03-01 11:24         ` Steven Price
2019-02-27 17:06 ` [PATCH v3 28/34] mm: pagewalk: Add test_p?d callbacks Steven Price
2019-02-27 17:06 ` [PATCH v3 29/34] arm64: mm: Convert mm/dump.c to use walk_page_range() Steven Price
2019-02-27 17:06 ` [PATCH v3 30/34] x86/mm: Point to struct seq_file from struct pg_state Steven Price
2019-02-27 17:06 ` [PATCH v3 31/34] x86/mm+efi: Convert ptdump_walk_pgd_level() to take a mm_struct Steven Price
2019-02-27 17:06 ` [PATCH v3 32/34] x86/mm: Convert ptdump_walk_pgd_level_debugfs() to take an mm_struct Steven Price
2019-02-27 17:06 ` [PATCH v3 33/34] x86/mm: Convert ptdump_walk_pgd_level_core() " Steven Price
2019-02-27 17:06 ` [PATCH v3 34/34] x86: mm: Convert dump_pagetables to use walk_page_range Steven Price

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