LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Steven Price <steven.price@arm.com>, linux-mm@kvack.org
Cc: "Mark Rutland" <Mark.Rutland@arm.com>,
	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,
	"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 12/21] mm: pagewalk: Allow walking without vma
Date: Thu, 1 Aug 2019 12:11:05 +0530
Message-ID: <b43b68c5-8245-52cc-31b8-613dc299a469@arm.com> (raw)
In-Reply-To: <5aff70f7-67a5-c7e8-5fec-8182dea0da0c@arm.com>



On 07/29/2019 05:59 PM, Steven Price wrote:
> On 28/07/2019 15:20, Anshuman Khandual wrote:
>>
>>
>> On 07/22/2019 09:12 PM, Steven Price wrote:
>>> Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range
>>> for vma(VM_PFNMAP)", page_table_walk() will report any kernel area as
>>> a hole, because it lacks a vma.
>>>
>>> This means each arch has re-implemented page table walking when needed,
>>> for example in the per-arch ptdump walker.
>>>
>>> Remove the requirement to have a vma except when trying to split huge
>>> pages.
>>>
>>> Signed-off-by: Steven Price <steven.price@arm.com>
>>> ---
>>>  mm/pagewalk.c | 25 +++++++++++++++++--------
>>>  1 file changed, 17 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
>>> index 98373a9f88b8..1cbef99e9258 100644
>>> --- a/mm/pagewalk.c
>>> +++ b/mm/pagewalk.c
>>> @@ -36,7 +36,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
>>>  	do {
>>>  again:
>>>  		next = pmd_addr_end(addr, end);
>>> -		if (pmd_none(*pmd) || !walk->vma) {
>>> +		if (pmd_none(*pmd)) {
>>>  			if (walk->pte_hole)
>>>  				err = walk->pte_hole(addr, next, walk);
>>>  			if (err)
>>> @@ -59,9 +59,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
>>>  		if (!walk->pte_entry)
>>>  			continue;
>>>  
>>> -		split_huge_pmd(walk->vma, pmd, addr);
>>> -		if (pmd_trans_unstable(pmd))
>>> -			goto again;
>>> +		if (walk->vma) {
>>> +			split_huge_pmd(walk->vma, pmd, addr);
>>
>> Check for a PMD THP entry before attempting to split it ?
> 
> split_huge_pmd does the check for us:
>> #define split_huge_pmd(__vma, __pmd, __address)				\
>> 	do {								\
>> 		pmd_t *____pmd = (__pmd);				\
>> 		if (is_swap_pmd(*____pmd) || pmd_trans_huge(*____pmd)	\
>> 					|| pmd_devmap(*____pmd))	\
>> 			__split_huge_pmd(__vma, __pmd, __address,	\
>> 						false, NULL);		\
>> 	}  while (0)
> 
> And this isn't a change from the previous code - only that the entry is
> no longer split when walk->vma==NULL.

Does it make sense to name walk->vma check to differentiate between user
and kernel page tables. IMHO that will help make things clear and explicit
during page table walk.

> 
>>> +			if (pmd_trans_unstable(pmd))
>>> +				goto again;
>>> +		} else if (pmd_leaf(*pmd)) {
>>> +			continue;
>>> +		}
>>> +
>>>  		err = walk_pte_range(pmd, addr, next, walk);
>>>  		if (err)
>>>  			break;
>>> @@ -81,7 +86,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>>>  	do {
>>>   again:
>>>  		next = pud_addr_end(addr, end);
>>> -		if (pud_none(*pud) || !walk->vma) {
>>> +		if (pud_none(*pud)) {
>>>  			if (walk->pte_hole)
>>>  				err = walk->pte_hole(addr, next, walk);
>>>  			if (err)
>>> @@ -95,9 +100,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>>>  				break;
>>>  		}
>>>  
>>> -		split_huge_pud(walk->vma, pud, addr);
>>> -		if (pud_none(*pud))
>>> -			goto again;
>>> +		if (walk->vma) {
>>> +			split_huge_pud(walk->vma, pud, addr);
>>
>> Check for a PUD THP entry before attempting to split it ?
> 
> Same as above.
> 
>>> +			if (pud_none(*pud))
>>> +				goto again;
>>> +		} else if (pud_leaf(*pud)) {
>>> +			continue;
>>> +		}
>>
>> This is bit cryptic. walk->vma check should be inside a helper is_user_page_table()
>> or similar to make things clear. p4d_leaf() check missing in walk_p4d_range() for
>> kernel page table walk ? Wondering if p?d_leaf() test should be moved earlier while
>> calling p?d_entry() for kernel page table walk.
> 
> I wasn't sure if it was worth putting p4d_leaf() and pgd_leaf() checks
> in (yet). No architecture that I know of uses such large pages.

Just to be complete it does make sense to add the remaining possible leaf
entry checks but will leave it upto you.

> 
> I'm not sure what you mean by moving the p?d_leaf() test earlier? Can
> you explain with an example?

In case its a kernel p?d_leaf() entry, then there is nothing to be done
after calling respective walk->p?d_entry() functions. Hence this check
should not complement user page table check (walk->vma) later in the
function but instead be checked right after walk->p?d_entry(). But its
not a big deal I guess.

  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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=b43b68c5-8245-52cc-31b8-613dc299a469@arm.com \
    --to=anshuman.khandual@arm.com \
    --cc=Mark.Rutland@arm.com \
    --cc=akpm@linux-foundation.org \
    --cc=ard.biesheuvel@linaro.org \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=catalin.marinas@arm.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=hpa@zytor.com \
    --cc=james.morse@arm.com \
    --cc=jglisse@redhat.com \
    --cc=kan.liang@linux.intel.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=luto@kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=steven.price@arm.com \
    --cc=tglx@linutronix.de \
    --cc=will@kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
	git clone --mirror https://lore.kernel.org/lkml/10 lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git