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From: Steven Price <steven.price@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: 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>,
	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>,
	"Will Deacon" <will@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org, "Liang,
	Kan" <kan.liang@linux.intel.com>
Subject: Re: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry()
Date: Wed, 24 Jul 2019 14:53:04 +0100
Message-ID: <60ee20ef-62a3-5df1-6e24-24973b69be70@arm.com> (raw)
In-Reply-To: <20190723101432.GC8085@lakrids.cambridge.arm.com>

On 23/07/2019 11:14, Mark Rutland wrote:
> On Mon, Jul 22, 2019 at 04:42:00PM +0100, Steven Price wrote:
>> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410
>> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were
>> no users. We're about to add users so reintroduce them, along with
>> p4d_entry() as we now have 5 levels of tables.
>>
>> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for
>> PUD-sized transparent hugepages") already re-added pud_entry() but with
>> different semantics to the other callbacks. Since there have never
>> been upstream users of this, revert the semantics back to match the
>> other callbacks. This means pud_entry() is called for all entries, not
>> just transparent huge pages.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>  include/linux/mm.h | 15 +++++++++------
>>  mm/pagewalk.c      | 27 ++++++++++++++++-----------
>>  2 files changed, 25 insertions(+), 17 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 0334ca97c584..b22799129128 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
>>  
>>  /**
>>   * mm_walk - callbacks for walk_page_range
>> - * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry
>> - *	       this handler should only handle pud_trans_huge() puds.
>> - *	       the pmd_entry or pte_entry callbacks will be used for
>> - *	       regular PUDs.
>> - * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
>> + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry
>> + * @p4d_entry: if set, called for each non-empty P4D entry
>> + * @pud_entry: if set, called for each non-empty PUD entry
>> + * @pmd_entry: if set, called for each non-empty PMD entry
> 
> How are these expected to work with folding?
> 
> For example, on arm64 with 64K pages and 42-bit VA, you can have 2-level
> tables where the PGD is P4D, PUD, and PMD. IIUC we'd invoke the
> callbacks for each of those levels where we found an entry in the pgd.
> 
> Either the callee handle that, or we should inhibit the callbacks when
> levels are folded, and I think that needs to be explcitly stated either
> way.
> 
> IIRC on x86 the p4d folding is dynamic depending on whether the HW
> supports 5-level page tables. Maybe that implies the callee has to
> handle that.

Yes, my assumption is that it has to be up to the callee to handle that
because folding can be dynamic. I believe this also was how these
callbacks work before they were removed. However I'll add a comment
explaining that here as it's probably non-obvious.

Steve

  reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-22 15:41 [PATCH v9 00/21] Generic page walk and ptdump Steven Price
2019-07-22 15:41 ` [PATCH v9 01/21] arc: mm: Add p?d_leaf() definitions Steven Price
2019-07-22 15:41 ` [PATCH v9 02/21] arm: " Steven Price
2019-07-22 15:41 ` [PATCH v9 03/21] arm64: " Steven Price
2019-07-22 15:41 ` [PATCH v9 04/21] mips: " Steven Price
2019-07-22 21:47   ` Paul Burton
2019-07-24 13:03     ` Steven Price
2019-07-22 15:41 ` [PATCH v9 05/21] powerpc: " Steven Price
2019-07-22 15:41 ` [PATCH v9 06/21] riscv: " Steven Price
2019-07-22 15:41 ` [PATCH v9 07/21] s390: " Steven Price
2019-07-22 15:41 ` [PATCH v9 08/21] sparc: " Steven Price
2019-07-22 15:41 ` [PATCH v9 09/21] x86: " Steven Price
2019-07-22 15:41 ` [PATCH v9 10/21] mm: Add generic p?d_leaf() macros Steven Price
2019-07-23  9:41   ` Mark Rutland
2019-07-24 13:48     ` Steven Price
2019-07-28 11:44     ` Anshuman Khandual
2019-07-29 11:38       ` Steven Price
2019-08-01  6:09         ` Anshuman Khandual
2019-08-01 12:22           ` Steven Price
2019-07-29 12:50       ` Mark Rutland
2019-08-01  6:13         ` Anshuman Khandual
2019-07-22 15:42 ` [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry() Steven Price
2019-07-23 10:14   ` Mark Rutland
2019-07-24 13:53     ` Steven Price [this message]
2019-07-24 14:09       ` Mark Rutland
2019-07-28 12:33   ` Anshuman Khandual
2019-07-29 12:17     ` Steven Price
2019-07-22 15:42 ` [PATCH v9 12/21] mm: pagewalk: Allow walking without vma Steven Price
2019-07-28 14:20   ` Anshuman Khandual
2019-07-29 12:29     ` Steven Price
2019-08-01  6:41       ` Anshuman Khandual
2019-07-22 15:42 ` [PATCH v9 13/21] mm: pagewalk: Add test_p?d callbacks Steven Price
2019-07-28 13:41   ` Anshuman Khandual
2019-07-29 12:34     ` Steven Price
2019-07-22 15:42 ` [PATCH v9 14/21] x86: mm: Don't display pages which aren't present in debugfs Steven Price
2019-07-22 15:42 ` [PATCH v9 15/21] x86: mm: Point to struct seq_file from struct pg_state Steven Price
2019-07-22 15:42 ` [PATCH v9 16/21] x86: mm+efi: Convert ptdump_walk_pgd_level() to take a mm_struct Steven Price
2019-07-22 15:42 ` [PATCH v9 17/21] x86: mm: Convert ptdump_walk_pgd_level_debugfs() to take an mm_struct Steven Price
2019-07-22 15:42 ` [PATCH v9 18/21] x86: mm: Convert ptdump_walk_pgd_level_core() " Steven Price
2019-07-22 15:42 ` [PATCH v9 19/21] mm: Add generic ptdump Steven Price
2019-07-23  9:57   ` Mark Rutland
2019-07-24 16:36     ` Steven Price
2019-07-29  2:59   ` Anshuman Khandual
2019-07-29 13:56     ` Steven Price
2019-07-22 15:42 ` [PATCH v9 20/21] x86: mm: Convert dump_pagetables to use walk_page_range Steven Price
2019-07-22 15:42 ` [PATCH v9 21/21] arm64: mm: Convert mm/dump.c to use walk_page_range() Steven Price
2019-07-23  6:39 ` [PATCH v9 00/21] Generic page walk and ptdump Anshuman Khandual
2019-07-24 13:35   ` Steven Price
2019-07-25  9:09     ` Anshuman Khandual
2019-07-25  9:30       ` Will Deacon
2019-07-26  6:03         ` Anshuman Khandual
2019-07-25 10:15       ` Steven Price
2019-07-23 10:16 ` Mark Rutland
2019-07-24 13:35   ` Steven Price
2019-07-24 13:57     ` Thomas Gleixner
2019-07-24 14:07       ` Mark Rutland
2019-07-24 14:18       ` Steven Price
2019-07-24 14:37         ` Thomas Gleixner
2019-07-28 11:20 ` Anshuman Khandual
2019-07-29 11:32   ` Steven Price
2019-07-31  9:27     ` Sven Schnelle
2019-07-31 11:18       ` Steven Price

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