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FROMLIST: mm: provide speculative fault infrastructure

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Provide infrastructure to do a speculative fault (not holding
mmap_sem).

The not holding of mmap_sem means we can race against VMA
change/removal and page-table destruction. We use the SRCU VMA freeing
to keep the VMA around. We use the VMA seqcount to detect change
(including umapping / page-table deletion) and we use gup_fast() style
page-table walking to deal with page-table races.

Once we've obtained the page and are ready to update the PTE, we
validate if the state we started the fault with is still valid, if
not, we'll fail the fault with VM_FAULT_RETRY, otherwise we update the
PTE and we're done.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

[Manage the newly introduced pte_spinlock() for speculative page
 fault to fail if the VMA is touched in our back]
[Rename vma_is_dead() to vma_has_changed() and declare it here]
[Fetch p4d and pud]
[Set vmd.sequence in __handle_mm_fault()]
[Abort speculative path when handle_userfault() has to be called]
[Add additional VMA's flags checks in handle_speculative_fault()]
[Clear FAULT_FLAG_ALLOW_RETRY in handle_speculative_fault()]
[Don't set vmf->pte and vmf->ptl if pte_map_lock() failed]
[Remove warning comment about waiting for !seq&1 since we don't want
 to wait]
[Remove warning about no huge page support, mention it explictly]
[Don't call do_fault() in the speculative path as __do_fault() calls
 vma->vm_ops->fault() which may want to release mmap_sem]
[Only vm_fault pointer argument for vma_has_changed()]
[Fix check against huge page, calling pmd_trans_huge()]
[Use READ_ONCE() when reading VMA's fields in the speculative path]
[Explicitly check for __HAVE_ARCH_PTE_SPECIAL as we can't support for
 processing done in vm_normal_page()]
[Check that vma->anon_vma is already set when starting the speculative
 path]
[Check for memory policy as we can't support MPOL_INTERLEAVE case due to
 the processing done in mpol_misplaced()]
[Don't support VMA growing up or down]
[Move check on vm_sequence just before calling handle_pte_fault()]
[Don't build SPF services if !CONFIG_SPECULATIVE_PAGE_FAULT]
[Add mem cgroup oom check]
[Use READ_ONCE to access p*d entries]
[Replace deprecated ACCESS_ONCE() by READ_ONCE() in vma_has_changed()]
[Don't fetch pte again in handle_pte_fault() when running the speculative
 path]
[Check PMD against concurrent collapsing operation]
[Try spin lock the pte during the speculative path to avoid deadlock with
 other CPU's invalidating the TLB and requiring this CPU to catch the
 inter processor's interrupt]
[Move define of FAULT_FLAG_SPECULATIVE here]
[Introduce __handle_speculative_fault() and add a check against
 mm->mm_users in handle_speculative_fault() defined in mm.h]
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Link: https://lore.kernel.org/lkml/1523975611-15978-19-git-send-email-ldufour@linux.vnet.ibm.com/
Bug: 161210518
Change-Id: I6a29e6edd9779bd34a9f7f4f6034e041a8487f30
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
This commit is contained in:
Peter Zijlstra
2018-04-17 16:33:24 +02:00
committed by Suren Baghdasaryan
parent 6d8fc36d9e
commit 1c53717440
5 changed files with 386 additions and 7 deletions
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31
include/linux/mm.h
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@@ -465,6 +465,8 @@ extern pgprot_t protection_map[16];
#define FAULT_FLAG_REMOTE 0x80
#define FAULT_FLAG_INSTRUCTION 0x100
#define FAULT_FLAG_INTERRUPTIBLE 0x200
/* Speculative fault, not holding mmap_sem */
#define FAULT_FLAG_SPECULATIVE 0x400
/*
* The default fault flags that should be used by most of the
@@ -520,6 +522,10 @@ struct vm_fault {
gfp_t gfp_mask; /* gfp mask to be used for allocations */
pgoff_t pgoff; /* Logical page offset based on vma */
unsigned long address; /* Faulting virtual address */
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
unsigned int sequence;
pmd_t orig_pmd; /* value of PMD at the time of fault */
#endif
pmd_t *pmd; /* Pointer to pmd entry matching
* the 'address' */
pud_t *pud; /* Pointer to pud entry matching
@@ -1760,6 +1766,31 @@ extern vm_fault_t handle_mm_fault(struct vm_area_struct *vma,
extern int fixup_user_fault(struct mm_struct *mm,
unsigned long address, unsigned int fault_flags,
bool *unlocked);
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
extern int __handle_speculative_fault(struct mm_struct *mm,
unsigned long address,
unsigned int flags);
static inline int handle_speculative_fault(struct mm_struct *mm,
unsigned long address,
unsigned int flags)
{
/*
* Try speculative page fault for multithreaded user space task only.
*/
if (!(flags & FAULT_FLAG_USER) || atomic_read(&mm->mm_users) == 1)
return VM_FAULT_RETRY;
return __handle_speculative_fault(mm, address, flags);
}
#else
static inline int handle_speculative_fault(struct mm_struct *mm,
unsigned long address,
unsigned int flags)
{
return VM_FAULT_RETRY;
}
#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
void unmap_mapping_pages(struct address_space *mapping,
pgoff_t start, pgoff_t nr, bool even_cows);
void unmap_mapping_range(struct address_space *mapping,