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From: Mark Rutland <mark.rutland@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: linux-mm@kvack.org, "Andy Lutomirski" <luto@kernel.org>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Arnd Bergmann" <arnd@arndb.de>, "Borislav Petkov" <bp@alien8.de>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"James Morse" <james.morse@arm.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Will Deacon" <will@kernel.org>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, "Liang,
	Kan" <kan.liang@linux.intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry()
Date: Tue, 23 Jul 2019 11:14:33 +0100
Message-ID: <20190723101432.GC8085@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190722154210.42799-12-steven.price@arm.com>

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.

Thanks,
Mark.


>   *	       this handler is required to be able to handle
>   *	       pmd_trans_huge() pmds.  They may simply choose to
>   *	       split_huge_page() instead of handling it explicitly.
> - * @pte_entry: if set, called for each non-empty PTE (4th-level) entry
> + * @pte_entry: if set, called for each non-empty PTE (lowest-level) entry
>   * @pte_hole: if set, called for each hole at all levels
>   * @hugetlb_entry: if set, called for each hugetlb entry
>   * @test_walk: caller specific callback function to determine whether
> @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
>   * (see the comment on walk_page_range() for more details)
>   */
>  struct mm_walk {
> +	int (*pgd_entry)(pgd_t *pgd, unsigned long addr,
> +			 unsigned long next, struct mm_walk *walk);
> +	int (*p4d_entry)(p4d_t *p4d, unsigned long addr,
> +			 unsigned long next, struct mm_walk *walk);
>  	int (*pud_entry)(pud_t *pud, unsigned long addr,
>  			 unsigned long next, struct mm_walk *walk);
>  	int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index c3084ff2569d..98373a9f88b8 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>  		}
>  
>  		if (walk->pud_entry) {
> -			spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
> -
> -			if (ptl) {
> -				err = walk->pud_entry(pud, addr, next, walk);
> -				spin_unlock(ptl);
> -				if (err)
> -					break;
> -				continue;
> -			}
> +			err = walk->pud_entry(pud, addr, next, walk);
> +			if (err)
> +				break;
>  		}
>  
>  		split_huge_pud(walk->vma, pud, addr);
> @@ -131,7 +125,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
>  				break;
>  			continue;
>  		}
> -		if (walk->pmd_entry || walk->pte_entry)
> +		if (walk->p4d_entry) {
> +			err = walk->p4d_entry(p4d, addr, next, walk);
> +			if (err)
> +				break;
> +		}
> +		if (walk->pud_entry || walk->pmd_entry || walk->pte_entry)
>  			err = walk_pud_range(p4d, addr, next, walk);
>  		if (err)
>  			break;
> @@ -157,7 +156,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
>  				break;
>  			continue;
>  		}
> -		if (walk->pmd_entry || walk->pte_entry)
> +		if (walk->pgd_entry) {
> +			err = walk->pgd_entry(pgd, addr, next, walk);
> +			if (err)
> +				break;
> +		}
> +		if (walk->p4d_entry || walk->pud_entry || walk->pmd_entry ||
> +				walk->pte_entry)
>  			err = walk_p4d_range(pgd, addr, next, walk);
>  		if (err)
>  			break;
> -- 
> 2.20.1
> 

  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 [this message]
2019-07-24 13:53     ` Steven Price
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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