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
>>
>
next prev parent reply other threads:[~2018-04-30 14:07 UTC|newest]
Thread overview: 60+ 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
2018-05-04 15:55 ` Punit Agrawal
2018-04-17 14:33 ` [PATCH v10 25/25] powerpc/mm: add speculative page fault Laurent Dufour
2018-04-17 16:51 ` [PATCH v10 00/25] Speculative page faults Christopher Lameter
2018-05-02 14:17 ` Punit Agrawal
2018-05-02 14:45 ` Laurent Dufour
2018-05-02 15:50 ` Punit Agrawal
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