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From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
To: Minchan Kim <minchan@kernel.org>
Cc: akpm@linux-foundation.org, mhocko@kernel.org,
	peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com,
	dave@stgolabs.net, jack@suse.cz,
	Matthew Wilcox <willy@infradead.org>,
	benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	hpa@zytor.com, Will Deacon <will.deacon@arm.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	David Rientjes <rientjes@google.com>,
	Jerome Glisse <jglisse@redhat.com>,
	Ganesh Mahendran <opensource.ganesh@gmail.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com,
	npiggin@gmail.com, bsingharora@gmail.com,
	paulmck@linux.vnet.ibm.com, Tim Chen <tim.c.chen@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v10 06/25] mm: make pte_unmap_same compatible with SPF
Date: Mon, 30 Apr 2018 16:07:30 +0200	[thread overview]
Message-ID: <dd5c4338-3cbb-c65a-f0c1-c71e2a0037ee@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180423063157.GB114098@rodete-desktop-imager.corp.google.com>

On 23/04/2018 08:31, Minchan Kim wrote:
> On Tue, Apr 17, 2018 at 04:33:12PM +0200, Laurent Dufour wrote:
>> pte_unmap_same() is making the assumption that the page table are still
>> around because the mmap_sem is held.
>> This is no more the case when running a speculative page fault and
>> additional check must be made to ensure that the final page table are still
>> there.
>>
>> This is now done by calling pte_spinlock() to check for the VMA's
>> consistency while locking for the page tables.
>>
>> This is requiring passing a vm_fault structure to pte_unmap_same() which is
>> containing all the needed parameters.
>>
>> As pte_spinlock() may fail in the case of a speculative page fault, if the
>> VMA has been touched in our back, pte_unmap_same() should now return 3
>> cases :
>> 	1. pte are the same (0)
>> 	2. pte are different (VM_FAULT_PTNOTSAME)
>> 	3. a VMA's changes has been detected (VM_FAULT_RETRY)
>>
>> The case 2 is handled by the introduction of a new VM_FAULT flag named
>> VM_FAULT_PTNOTSAME which is then trapped in cow_user_page().
> 
> I don't see such logic in this patch.
> Maybe you introduces it later? If so, please comment on it.
> Or just return 0 in case of 2 without introducing VM_FAULT_PTNOTSAME.

Late in the series, pte_spinlock() will check for the VMA's changes and may
return 1. This will be then required to handle the 3 cases presented above.

I can move this handling later in the series, but I wondering if this will make
it more easier to read.

> 
>> If VM_FAULT_RETRY is returned, it is passed up to the callers to retry the
>> page fault while holding the mmap_sem.
>>
>> Acked-by: David Rientjes <rientjes@google.com>
>> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
>> ---
>>  include/linux/mm.h |  1 +
>>  mm/memory.c        | 39 ++++++++++++++++++++++++++++-----------
>>  2 files changed, 29 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 4d1aff80669c..714da99d77a3 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1208,6 +1208,7 @@ static inline void clear_page_pfmemalloc(struct page *page)
>>  #define VM_FAULT_NEEDDSYNC  0x2000	/* ->fault did not modify page tables
>>  					 * and needs fsync() to complete (for
>>  					 * synchronous page faults in DAX) */
>> +#define VM_FAULT_PTNOTSAME 0x4000	/* Page table entries have changed */
>>  
>>  #define VM_FAULT_ERROR	(VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
>>  			 VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 0b9a51f80e0e..f86efcb8e268 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2309,21 +2309,29 @@ static inline bool pte_map_lock(struct vm_fault *vmf)
>>   * parts, do_swap_page must check under lock before unmapping the pte and
>>   * proceeding (but do_wp_page is only called after already making such a check;
>>   * and do_anonymous_page can safely check later on).
>> + *
>> + * pte_unmap_same() returns:
>> + *	0			if the PTE are the same
>> + *	VM_FAULT_PTNOTSAME	if the PTE are different
>> + *	VM_FAULT_RETRY		if the VMA has changed in our back during
>> + *				a speculative page fault handling.
>>   */
>> -static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
>> -				pte_t *page_table, pte_t orig_pte)
>> +static inline int pte_unmap_same(struct vm_fault *vmf)
>>  {
>> -	int same = 1;
>> +	int ret = 0;
>> +
>>  #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
>>  	if (sizeof(pte_t) > sizeof(unsigned long)) {
>> -		spinlock_t *ptl = pte_lockptr(mm, pmd);
>> -		spin_lock(ptl);
>> -		same = pte_same(*page_table, orig_pte);
>> -		spin_unlock(ptl);
>> +		if (pte_spinlock(vmf)) {
>> +			if (!pte_same(*vmf->pte, vmf->orig_pte))
>> +				ret = VM_FAULT_PTNOTSAME;
>> +			spin_unlock(vmf->ptl);
>> +		} else
>> +			ret = VM_FAULT_RETRY;
>>  	}
>>  #endif
>> -	pte_unmap(page_table);
>> -	return same;
>> +	pte_unmap(vmf->pte);
>> +	return ret;
>>  }
>>  
>>  static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
>> @@ -2912,10 +2920,19 @@ int do_swap_page(struct vm_fault *vmf)
>>  	pte_t pte;
>>  	int locked;
>>  	int exclusive = 0;
>> -	int ret = 0;
>> +	int ret;
>>  
>> -	if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
>> +	ret = pte_unmap_same(vmf);
>> +	if (ret) {
>> +		/*
>> +		 * If pte != orig_pte, this means another thread did the
>> +		 * swap operation in our back.
>> +		 * So nothing else to do.
>> +		 */
>> +		if (ret == VM_FAULT_PTNOTSAME)
>> +			ret = 0;
>>  		goto out;
>> +	}
>>  
>>  	entry = pte_to_swp_entry(vmf->orig_pte);
>>  	if (unlikely(non_swap_entry(entry))) {
>> -- 
>> 2.7.4
>>
> 

  reply	other threads:[~2018-04-30 14:07 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-17 14:33 [PATCH v10 00/25] Speculative page faults Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 01/25] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT Laurent Dufour
2018-04-23  5:58   ` Minchan Kim
2018-04-23 15:10     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 02/25] x86/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT Laurent Dufour
2018-05-08 11:04   ` Punit Agrawal
2018-05-14 14:47     ` Laurent Dufour
2018-05-14 15:05       ` Punit Agrawal
2018-04-17 14:33 ` [PATCH v10 03/25] powerpc/mm: set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 04/25] mm: prepare for FAULT_FLAG_SPECULATIVE Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 05/25] mm: introduce pte_spinlock " Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 06/25] mm: make pte_unmap_same compatible with SPF Laurent Dufour
2018-04-23  6:31   ` Minchan Kim
2018-04-30 14:07     ` Laurent Dufour [this message]
2018-05-01 13:04       ` Minchan Kim
2018-05-10 16:15   ` vinayak menon
2018-05-14 15:09     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 07/25] mm: introduce INIT_VMA() Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 08/25] mm: VMA sequence count Laurent Dufour
2018-04-23  6:42   ` Minchan Kim
2018-04-30 15:14     ` Laurent Dufour
2018-05-01 13:16       ` Minchan Kim
2018-05-03 14:45         ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 09/25] mm: protect VMA modifications using " Laurent Dufour
2018-04-23  7:19   ` Minchan Kim
2018-05-14 15:25     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 10/25] mm: protect mremap() against SPF hanlder Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 11/25] mm: protect SPF handler against anon_vma changes Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 12/25] mm: cache some VMA fields in the vm_fault structure Laurent Dufour
2018-04-23  7:42   ` Minchan Kim
2018-05-03 12:25     ` Laurent Dufour
2018-05-03 15:42       ` Minchan Kim
2018-05-04  9:10         ` Laurent Dufour
2018-05-08 10:56           ` Minchan Kim
2018-04-17 14:33 ` [PATCH v10 13/25] mm/migrate: Pass vm_fault pointer to migrate_misplaced_page() Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 14/25] mm: introduce __lru_cache_add_active_or_unevictable Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 15/25] mm: introduce __vm_normal_page() Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 16/25] mm: introduce __page_add_new_anon_rmap() Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 17/25] mm: protect mm_rb tree with a rwlock Laurent Dufour
2018-04-30 18:47   ` Punit Agrawal
2018-05-02  6:37     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 18/25] mm: provide speculative fault infrastructure Laurent Dufour
2018-05-15 13:09   ` vinayak menon
2018-05-15 14:07     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 19/25] mm: adding speculative page fault failure trace events Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 20/25] perf: add a speculative page fault sw event Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 21/25] perf tools: add support for the SPF perf event Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 22/25] mm: speculative page fault handler return VMA Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 23/25] mm: add speculative page fault vmstats Laurent Dufour
2018-05-16  2:50   ` Ganesh Mahendran
2018-05-16  6:42     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 24/25] x86/mm: add speculative pagefault handling Laurent Dufour
2018-04-30 18:43   ` Punit Agrawal
2018-05-03 14:59     ` Laurent Dufour
2018-04-17 14:33 ` [PATCH v10 25/25] powerpc/mm: add speculative page fault Laurent Dufour
2018-05-02 14:17 ` [PATCH v10 00/25] Speculative page faults Punit Agrawal
2018-05-02 14:45   ` Laurent Dufour

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