From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
To: paulmck@linux.vnet.ibm.com, peterz@infradead.org,
akpm@linux-foundation.org, kirill@shutemov.name,
ak@linux.intel.com, mhocko@kernel.org, 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>
Cc: 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,
Tim Chen <tim.c.chen@linux.intel.com>,
linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: [PATCH v7 04/24] mm: Dont assume page-table invariance during faults
Date: Tue, 6 Feb 2018 17:49:50 +0100 [thread overview]
Message-ID: <1517935810-31177-5-git-send-email-ldufour@linux.vnet.ibm.com> (raw)
In-Reply-To: <1517935810-31177-1-git-send-email-ldufour@linux.vnet.ibm.com>
From: Peter Zijlstra <peterz@infradead.org>
One of the side effects of speculating on faults (without holding
mmap_sem) is that we can race with free_pgtables() and therefore we
cannot assume the page-tables will stick around.
Remove the reliance on the pte pointer.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
In most of the case pte_unmap_same() was returning 1, which meaning that
do_swap_page() should do its processing. So in most of the case there will
be no impact.
Now regarding the case where pte_unmap_safe() was returning 0, and thus
do_swap_page return 0 too, this happens when the page has already been
swapped back. This may happen before do_swap_page() get called or while in
the call to do_swap_page(). In that later case, the check done when
swapin_readahead() returns will detect that case.
The worst case would be that a page fault is occuring on 2 threads at the
same time on the same swapped out page. In that case one thread will take
much time looping in __read_swap_cache_async(). But in the regular page
fault path, this is even worse since the thread would wait for semaphore to
be released before starting anything.
[Remove only if !CONFIG_SPECULATIVE_PAGE_FAULT]
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
mm/memory.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c
index 5ec6433d6a5c..32b9eb77d95c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2288,6 +2288,7 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
}
EXPORT_SYMBOL_GPL(apply_to_page_range);
+#ifndef CONFIG_SPECULATIVE_PAGE_FAULT
/*
* handle_pte_fault chooses page fault handler according to an entry which was
* read non-atomically. Before making any commitment, on those architectures
@@ -2311,6 +2312,7 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
pte_unmap(page_table);
return same;
}
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
{
@@ -2898,11 +2900,13 @@ int do_swap_page(struct vm_fault *vmf)
swapcache = page;
}
+#ifndef CONFIG_SPECULATIVE_PAGE_FAULT
if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) {
if (page)
put_page(page);
goto out;
}
+#endif
entry = pte_to_swp_entry(vmf->orig_pte);
if (unlikely(non_swap_entry(entry))) {
--
2.7.4
next prev parent reply other threads:[~2018-02-06 16:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-06 16:49 [PATCH v7 00/24] Speculative page faults Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 01/24] mm: Introduce CONFIG_SPECULATIVE_PAGE_FAULT Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 02/24] x86/mm: Define CONFIG_SPECULATIVE_PAGE_FAULT Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 03/24] powerpc/mm: " Laurent Dufour
2018-02-06 16:49 ` Laurent Dufour [this message]
2018-02-06 20:28 ` [PATCH v7 04/24] mm: Dont assume page-table invariance during faults Matthew Wilcox
2018-02-08 14:35 ` Laurent Dufour
2018-02-08 15:00 ` Matthew Wilcox
2018-02-08 17:14 ` Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 05/24] mm: Prepare for FAULT_FLAG_SPECULATIVE Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 06/24] mm: Introduce pte_spinlock " Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 07/24] mm: VMA sequence count Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 08/24] mm: Protect VMA modifications using " Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 09/24] mm: protect mremap() against SPF hanlder Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 10/24] mm: Protect SPF handler against anon_vma changes Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 11/24] mm: Cache some VMA fields in the vm_fault structure Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 12/24] mm/migrate: Pass vm_fault pointer to migrate_misplaced_page() Laurent Dufour
2018-02-06 16:49 ` [PATCH v7 13/24] mm: Introduce __lru_cache_add_active_or_unevictable Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 14/24] mm: Introduce __maybe_mkwrite() Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 15/24] mm: Introduce __vm_normal_page() Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 16/24] mm: Introduce __page_add_new_anon_rmap() Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 17/24] mm: Protect mm_rb tree with a rwlock Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 18/24] mm: Provide speculative fault infrastructure Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 19/24] mm: Adding speculative page fault failure trace events Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 20/24] perf: Add a speculative page fault sw event Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 21/24] perf tools: Add support for the SPF perf event Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 22/24] mm: Speculative page fault handler return VMA Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 23/24] x86/mm: Add speculative pagefault handling Laurent Dufour
2018-02-06 16:50 ` [PATCH v7 24/24] powerpc/mm: Add speculative page fault Laurent Dufour
2018-02-08 20:53 ` [PATCH v7 00/24] Speculative page faults Andrew Morton
2018-02-13 7:56 ` Laurent Dufour
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