lkml.org 
[lkml]   [2018]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v11 19/26] mm: provide speculative fault infrastructure
On 2018/7/25 0:10, Laurent Dufour wrote:
>
> On 24/07/2018 16:26, zhong jiang wrote:
>> On 2018/5/17 19:06, Laurent Dufour wrote:
>>> From: Peter Zijlstra <peterz@infradead.org>
>>>
>>> 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>
>>> ---
>>> include/linux/hugetlb_inline.h | 2 +-
>>> include/linux/mm.h | 30 ++++
>>> include/linux/pagemap.h | 4 +-
>>> mm/internal.h | 16 +-
>>> mm/memory.c | 340 ++++++++++++++++++++++++++++++++++++++++-
>>> 5 files changed, 385 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/hugetlb_inline.h b/include/linux/hugetlb_inline.h
>>> index 0660a03d37d9..9e25283d6fc9 100644
>>> --- a/include/linux/hugetlb_inline.h
>>> +++ b/include/linux/hugetlb_inline.h
>>> @@ -8,7 +8,7 @@
>>>
>>> static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma)
>>> {
>>> - return !!(vma->vm_flags & VM_HUGETLB);
>>> + return !!(READ_ONCE(vma->vm_flags) & VM_HUGETLB);
>>> }
>>>
>>> #else
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 05cbba70104b..31acf98a7d92 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -315,6 +315,7 @@ extern pgprot_t protection_map[16];
>>> #define FAULT_FLAG_USER 0x40 /* The fault originated in userspace */
>>> #define FAULT_FLAG_REMOTE 0x80 /* faulting for non current tsk/mm */
>>> #define FAULT_FLAG_INSTRUCTION 0x100 /* The fault was during an instruction fetch */
>>> +#define FAULT_FLAG_SPECULATIVE 0x200 /* Speculative fault, not holding mmap_sem */
>>>
>>> #define FAULT_FLAG_TRACE \
>>> { FAULT_FLAG_WRITE, "WRITE" }, \
>>> @@ -343,6 +344,10 @@ 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
>>> @@ -1415,6 +1420,31 @@ int invalidate_inode_page(struct page *page);
>>> #ifdef CONFIG_MMU
>>> extern int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>> unsigned int flags);
>>> +
>>> +#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 */
>>> +
>>> extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
>>> unsigned long address, unsigned int fault_flags,
>>> bool *unlocked);
>>> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
>>> index b1bd2186e6d2..6e2aa4e79af7 100644
>>> --- a/include/linux/pagemap.h
>>> +++ b/include/linux/pagemap.h
>>> @@ -456,8 +456,8 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
>>> pgoff_t pgoff;
>>> if (unlikely(is_vm_hugetlb_page(vma)))
>>> return linear_hugepage_index(vma, address);
>>> - pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
>>> - pgoff += vma->vm_pgoff;
>>> + pgoff = (address - READ_ONCE(vma->vm_start)) >> PAGE_SHIFT;
>>> + pgoff += READ_ONCE(vma->vm_pgoff);
>>> return pgoff;
>>> }
>>>
>>> diff --git a/mm/internal.h b/mm/internal.h
>>> index fb2667b20f0a..10b188c87fa4 100644
>>> --- a/mm/internal.h
>>> +++ b/mm/internal.h
>>> @@ -44,7 +44,21 @@ int do_swap_page(struct vm_fault *vmf);
>>> extern struct vm_area_struct *get_vma(struct mm_struct *mm,
>>> unsigned long addr);
>>> extern void put_vma(struct vm_area_struct *vma);
>>> -#endif
>>> +
>>> +static inline bool vma_has_changed(struct vm_fault *vmf)
>>> +{
>>> + int ret = RB_EMPTY_NODE(&vmf->vma->vm_rb);
>>> + unsigned int seq = READ_ONCE(vmf->vma->vm_sequence.sequence);
>>> +
>>> + /*
>>> + * Matches both the wmb in write_seqlock_{begin,end}() and
>>> + * the wmb in vma_rb_erase().
>>> + */
>>> + smp_rmb();
>>> +
>>> + return ret || seq != vmf->sequence;
>>> +}
>>> +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
>>>
>>> void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
>>> unsigned long floor, unsigned long ceiling);
>>> diff --git a/mm/memory.c b/mm/memory.c
>>> index ab32b0b4bd69..7bbbb8c7b9cd 100644
>>> --- a/mm/memory.c
>>> +++ b/mm/memory.c
>>> @@ -769,7 +769,8 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
>>> if (page)
>>> dump_page(page, "bad pte");
>>> pr_alert("addr:%p vm_flags:%08lx anon_vma:%p mapping:%p index:%lx\n",
>>> - (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
>>> + (void *)addr, READ_ONCE(vma->vm_flags), vma->anon_vma,
>>> + mapping, index);
>>> pr_alert("file:%pD fault:%pf mmap:%pf readpage:%pf\n",
>>> vma->vm_file,
>>> vma->vm_ops ? vma->vm_ops->fault : NULL,
>>> @@ -2306,6 +2307,118 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>>> }
>>> EXPORT_SYMBOL_GPL(apply_to_page_range);
>>>
>>> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
>>> +static bool pte_spinlock(struct vm_fault *vmf)
>>> +{
>>> + bool ret = false;
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> + pmd_t pmdval;
>>> +#endif
>>> +
>>> + /* Check if vma is still valid */
>>> + if (!(vmf->flags & FAULT_FLAG_SPECULATIVE)) {
>>> + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>>> + spin_lock(vmf->ptl);
>>> + return true;
>>> + }
>>> +
>>> +again:
>>> + local_irq_disable();
>>> + if (vma_has_changed(vmf))
>>> + goto out;
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> + /*
>>> + * We check if the pmd value is still the same to ensure that there
>>> + * is not a huge collapse operation in progress in our back.
>>> + */
>>> + pmdval = READ_ONCE(*vmf->pmd);
>>> + if (!pmd_same(pmdval, vmf->orig_pmd))
>>> + goto out;
>>> +#endif
>>> +
>>> + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>>> + if (unlikely(!spin_trylock(vmf->ptl))) {
>>> + local_irq_enable();
>>> + goto again;
>>> + }
>>> +
>>> + if (vma_has_changed(vmf)) {
>>> + spin_unlock(vmf->ptl);
>>> + goto out;
>>> + }
>>> +
>>> + ret = true;
>>> +out:
>>> + local_irq_enable();
>>> + return ret;
>>> +}
>>> +
>>> +static bool pte_map_lock(struct vm_fault *vmf)
>>> +{
>>> + bool ret = false;
>>> + pte_t *pte;
>>> + spinlock_t *ptl;
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> + pmd_t pmdval;
>>> +#endif
>>> +
>>> + if (!(vmf->flags & FAULT_FLAG_SPECULATIVE)) {
>>> + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
>>> + vmf->address, &vmf->ptl);
>>> + return true;
>>> + }
>>> +
>>> + /*
>>> + * The first vma_has_changed() guarantees the page-tables are still
>>> + * valid, having IRQs disabled ensures they stay around, hence the
>>> + * second vma_has_changed() to make sure they are still valid once
>>> + * we've got the lock. After that a concurrent zap_pte_range() will
>>> + * block on the PTL and thus we're safe.
>>> + */
>>> +again:
>>> + local_irq_disable();
>>> + if (vma_has_changed(vmf))
>>> + goto out;
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> + /*
>>> + * We check if the pmd value is still the same to ensure that there
>>> + * is not a huge collapse operation in progress in our back.
>>> + */
>>> + pmdval = READ_ONCE(*vmf->pmd);
>>> + if (!pmd_same(pmdval, vmf->orig_pmd))
>>> + goto out;
>>> +#endif
>>> +
>>> + /*
>>> + * Same as pte_offset_map_lock() except that we call
>>> + * spin_trylock() in place of spin_lock() to avoid race with
>>> + * unmap path which may have the lock and wait for this CPU
>>> + * to invalidate TLB but this CPU has irq disabled.
>>> + * Since we are in a speculative patch, accept it could fail
>>> + */
>>> + ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>>> + pte = pte_offset_map(vmf->pmd, vmf->address);
>>> + if (unlikely(!spin_trylock(ptl))) {
>>> + pte_unmap(pte);
>>> + local_irq_enable();
>>> + goto again;
>>> + }
>>> +
>>> + if (vma_has_changed(vmf)) {
>>> + pte_unmap_unlock(pte, ptl);
>>> + goto out;
>>> + }
>>> +
>>> + vmf->pte = pte;
>>> + vmf->ptl = ptl;
>>> + ret = true;
>>> +out:
>>> + local_irq_enable();
>>> + return ret;
>>> +}
>>> +#else
>>> static inline bool pte_spinlock(struct vm_fault *vmf)
>>> {
>>> vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>>> @@ -2319,6 +2432,7 @@ static inline bool pte_map_lock(struct vm_fault *vmf)
>>> vmf->address, &vmf->ptl);
>>> return true;
>>> }
>>> +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
>>>
>>> /*
>>> * handle_pte_fault chooses page fault handler according to an entry which was
>>> @@ -3208,6 +3322,14 @@ static int do_anonymous_page(struct vm_fault *vmf)
>>> ret = check_stable_address_space(vma->vm_mm);
>>> if (ret)
>>> goto unlock;
>>> + /*
>>> + * Don't call the userfaultfd during the speculative path.
>>> + * We already checked for the VMA to not be managed through
>>> + * userfaultfd, but it may be set in our back once we have lock
>>> + * the pte. In such a case we can ignore it this time.
>>> + */
>>> + if (vmf->flags & FAULT_FLAG_SPECULATIVE)
>>> + goto setpte;
>>> /* Deliver the page fault to userland, check inside PT lock */
>>> if (userfaultfd_missing(vma)) {
>>> pte_unmap_unlock(vmf->pte, vmf->ptl);
>>> @@ -3249,7 +3371,7 @@ static int do_anonymous_page(struct vm_fault *vmf)
>>> goto unlock_and_release;
>>>
>>> /* Deliver the page fault to userland, check inside PT lock */
>>> - if (userfaultfd_missing(vma)) {
>>> + if (!(vmf->flags & FAULT_FLAG_SPECULATIVE) && userfaultfd_missing(vma)) {
>>> pte_unmap_unlock(vmf->pte, vmf->ptl);
>>> mem_cgroup_cancel_charge(page, memcg, false);
>>> put_page(page);
>>> @@ -3994,13 +4116,22 @@ static int handle_pte_fault(struct vm_fault *vmf)
>>>
>>> if (unlikely(pmd_none(*vmf->pmd))) {
>>> /*
>>> + * In the case of the speculative page fault handler we abort
>>> + * the speculative path immediately as the pmd is probably
>>> + * in the way to be converted in a huge one. We will try
>>> + * again holding the mmap_sem (which implies that the collapse
>>> + * operation is done).
>>> + */
>>> + if (vmf->flags & FAULT_FLAG_SPECULATIVE)
>>> + return VM_FAULT_RETRY;
>>> + /*
>>> * Leave __pte_alloc() until later: because vm_ops->fault may
>>> * want to allocate huge page, and if we expose page table
>>> * for an instant, it will be difficult to retract from
>>> * concurrent faults and from rmap lookups.
>>> */
>>> vmf->pte = NULL;
>>> - } else {
>>> + } else if (!(vmf->flags & FAULT_FLAG_SPECULATIVE)) {
>>> /* See comment in pte_alloc_one_map() */
>>> if (pmd_devmap_trans_unstable(vmf->pmd))
>>> return 0;
>>> @@ -4009,6 +4140,9 @@ static int handle_pte_fault(struct vm_fault *vmf)
>>> * pmd from under us anymore at this point because we hold the
>>> * mmap_sem read mode and khugepaged takes it in write mode.
>>> * So now it's safe to run pte_offset_map().
>>> + * This is not applicable to the speculative page fault handler
>>> + * but in that case, the pte is fetched earlier in
>>> + * handle_speculative_fault().
>>> */
>>> vmf->pte = pte_offset_map(vmf->pmd, vmf->address);
>>> vmf->orig_pte = *vmf->pte;
>>> @@ -4031,6 +4165,8 @@ static int handle_pte_fault(struct vm_fault *vmf)
>>> if (!vmf->pte) {
>>> if (vma_is_anonymous(vmf->vma))
>>> return do_anonymous_page(vmf);
>>> + else if (vmf->flags & FAULT_FLAG_SPECULATIVE)
>>> + return VM_FAULT_RETRY;
>>> else
>>> return do_fault(vmf);
>>> }
>>> @@ -4128,6 +4264,9 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>> vmf.pmd = pmd_alloc(mm, vmf.pud, address);
>>> if (!vmf.pmd)
>>> return VM_FAULT_OOM;
>>> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
>>> + vmf.sequence = raw_read_seqcount(&vma->vm_sequence);
>>> +#endif
>>> if (pmd_none(*vmf.pmd) && transparent_hugepage_enabled(vma)) {
>>> ret = create_huge_pmd(&vmf);
>>> if (!(ret & VM_FAULT_FALLBACK))
>>> @@ -4161,6 +4300,201 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>> return handle_pte_fault(&vmf);
>>> }
>>>
>>> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
>>> +/*
>>> + * Tries to handle the page fault in a speculative way, without grabbing the
>>> + * mmap_sem.
>>> + */
>>> +int __handle_speculative_fault(struct mm_struct *mm, unsigned long address,
>>> + unsigned int flags)
>>> +{
>>> + struct vm_fault vmf = {
>>> + .address = address,
>>> + };
>>> + pgd_t *pgd, pgdval;
>>> + p4d_t *p4d, p4dval;
>>> + pud_t pudval;
>>> + int seq, ret = VM_FAULT_RETRY;
>>> + struct vm_area_struct *vma;
>>> +#ifdef CONFIG_NUMA
>>> + struct mempolicy *pol;
>>> +#endif
>>> +
>>> + /* Clear flags that may lead to release the mmap_sem to retry */
>>> + flags &= ~(FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_KILLABLE);
>>> + flags |= FAULT_FLAG_SPECULATIVE;
>>> +
>>> + vma = get_vma(mm, address);
>>> + if (!vma)
>>> + return ret;
>>> +
>>> + seq = raw_read_seqcount(&vma->vm_sequence); /* rmb <-> seqlock,vma_rb_erase() */
>>> + if (seq & 1)
>>> + goto out_put;
>>> +
>>> + /*
>>> + * Can't call vm_ops service has we don't know what they would do
>>> + * with the VMA.
>>> + * This include huge page from hugetlbfs.
>>> + */
>>> + if (vma->vm_ops)
>>> + goto out_put;
>>> +
>> Hi Laurent
>>
>> I think that most of pagefault will leave here. Is there any case need to skip ?
>> I have tested the following patch, it work well.
> Hi Zhong,
>
> Well this will allow file mapping to be handle in a speculative way, but that's
> a bit dangerous today as there is no guaranty that the vm_ops.vm_fault()
> operation will be fair.
>
> In the case of the anonymous file mapping that's often not a problem, depending
> on the underlying file system, but there are so many cases to check and this is
> hard to say this can be done in a speculative way as is.
This patch say that spf just handle anonyous page. but I find that do_swap_page
also maybe release the mmap_sem without FAULT_FLAG_RETRY_NOWAIT. why is it safe
to handle the case. I think that the case is similar to file page. Maybe I miss
something else.

I test the patches and find just only 18% of the pagefault will enter into the
speculative page fault during a process startup. As I had said. most of pagefault
will be handled by ops->fault. I do not know the data you had posted is how to get.


Thanks
zhong jiang
> The huge work to do is to double check that all the code called by
> vm_ops.fault() is not dealing with the mmap_sem, which could be handled using
> FAULT_FLAG_RETRY_NOWAIT, and care is also needed about the resources that code
> is managing as it may assume that it is under the protection of the mmap_sem in
> read mode, and that can be done implicitly.
>
> Cheers,
> Laurent.
>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 936128b..9bc1545 100644
>> @@ -3893,8 +3898,6 @@ static int handle_pte_fault(struct fault_env *fe)
>> if (!fe->pte) {
>> if (vma_is_anonymous(fe->vma))
>> return do_anonymous_page(fe);
>> - else if (fe->flags & FAULT_FLAG_SPECULATIVE)
>> - return VM_FAULT_RETRY;
>> else
>> return do_fault(fe);
>> }
>> @@ -4026,20 +4029,11 @@ int __handle_speculative_fault(struct mm_struct *mm, unsigned long address,
>> goto out_put;
>> }
>> /*
>> - * Can't call vm_ops service has we don't know what they would do
>> - * with the VMA.
>> - * This include huge page from hugetlbfs.
>> - */
>> - if (vma->vm_ops) {
>> - trace_spf_vma_notsup(_RET_IP_, vma, address);
>> - goto out_put;
>> - }
>>
>>
>> Thanks
>> zhong jiang
>>> + /*
>>> + * __anon_vma_prepare() requires the mmap_sem to be held
>>> + * because vm_next and vm_prev must be safe. This can't be guaranteed
>>> + * in the speculative path.
>>> + */
>>> + if (unlikely(!vma->anon_vma))
>>> + goto out_put;
>>> +
>>> + vmf.vma_flags = READ_ONCE(vma->vm_flags);
>>> + vmf.vma_page_prot = READ_ONCE(vma->vm_page_prot);
>>> +
>>> + /* Can't call userland page fault handler in the speculative path */
>>> + if (unlikely(vmf.vma_flags & VM_UFFD_MISSING))
>>> + goto out_put;
>>> +
>>> + if (vmf.vma_flags & VM_GROWSDOWN || vmf.vma_flags & VM_GROWSUP)
>>> + /*
>>> + * This could be detected by the check address against VMA's
>>> + * boundaries but we want to trace it as not supported instead
>>> + * of changed.
>>> + */
>>> + goto out_put;
>>> +
>>> + if (address < READ_ONCE(vma->vm_start)
>>> + || READ_ONCE(vma->vm_end) <= address)
>>> + goto out_put;
>>> +
>>> + if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
>>> + flags & FAULT_FLAG_INSTRUCTION,
>>> + flags & FAULT_FLAG_REMOTE)) {
>>> + ret = VM_FAULT_SIGSEGV;
>>> + goto out_put;
>>> + }
>>> +
>>> + /* This is one is required to check that the VMA has write access set */
>>> + if (flags & FAULT_FLAG_WRITE) {
>>> + if (unlikely(!(vmf.vma_flags & VM_WRITE))) {
>>> + ret = VM_FAULT_SIGSEGV;
>>> + goto out_put;
>>> + }
>>> + } else if (unlikely(!(vmf.vma_flags & (VM_READ|VM_EXEC|VM_WRITE)))) {
>>> + ret = VM_FAULT_SIGSEGV;
>>> + goto out_put;
>>> + }
>>> +
>>> +#ifdef CONFIG_NUMA
>>> + /*
>>> + * MPOL_INTERLEAVE implies additional checks in
>>> + * mpol_misplaced() which are not compatible with the
>>> + *speculative page fault processing.
>>> + */
>>> + pol = __get_vma_policy(vma, address);
>>> + if (!pol)
>>> + pol = get_task_policy(current);
>>> + if (pol && pol->mode == MPOL_INTERLEAVE)
>>> + goto out_put;
>>> +#endif
>>> +
>>> + /*
>>> + * Do a speculative lookup of the PTE entry.
>>> + */
>>> + local_irq_disable();
>>> + pgd = pgd_offset(mm, address);
>>> + pgdval = READ_ONCE(*pgd);
>>> + if (pgd_none(pgdval) || unlikely(pgd_bad(pgdval)))
>>> + goto out_walk;
>>> +
>>> + p4d = p4d_offset(pgd, address);
>>> + p4dval = READ_ONCE(*p4d);
>>> + if (p4d_none(p4dval) || unlikely(p4d_bad(p4dval)))
>>> + goto out_walk;
>>> +
>>> + vmf.pud = pud_offset(p4d, address);
>>> + pudval = READ_ONCE(*vmf.pud);
>>> + if (pud_none(pudval) || unlikely(pud_bad(pudval)))
>>> + goto out_walk;
>>> +
>>> + /* Huge pages at PUD level are not supported. */
>>> + if (unlikely(pud_trans_huge(pudval)))
>>> + goto out_walk;
>>> +
>>> + vmf.pmd = pmd_offset(vmf.pud, address);
>>> + vmf.orig_pmd = READ_ONCE(*vmf.pmd);
>>> + /*
>>> + * pmd_none could mean that a hugepage collapse is in progress
>>> + * in our back as collapse_huge_page() mark it before
>>> + * invalidating the pte (which is done once the IPI is catched
>>> + * by all CPU and we have interrupt disabled).
>>> + * For this reason we cannot handle THP in a speculative way since we
>>> + * can't safely indentify an in progress collapse operation done in our
>>> + * back on that PMD.
>>> + * Regarding the order of the following checks, see comment in
>>> + * pmd_devmap_trans_unstable()
>>> + */
>>> + if (unlikely(pmd_devmap(vmf.orig_pmd) ||
>>> + pmd_none(vmf.orig_pmd) || pmd_trans_huge(vmf.orig_pmd) ||
>>> + is_swap_pmd(vmf.orig_pmd)))
>>> + goto out_walk;
>>> +
>>> + /*
>>> + * The above does not allocate/instantiate page-tables because doing so
>>> + * would lead to the possibility of instantiating page-tables after
>>> + * free_pgtables() -- and consequently leaking them.
>>> + *
>>> + * The result is that we take at least one !speculative fault per PMD
>>> + * in order to instantiate it.
>>> + */
>>> +
>>> + vmf.pte = pte_offset_map(vmf.pmd, address);
>>> + vmf.orig_pte = READ_ONCE(*vmf.pte);
>>> + barrier(); /* See comment in handle_pte_fault() */
>>> + if (pte_none(vmf.orig_pte)) {
>>> + pte_unmap(vmf.pte);
>>> + vmf.pte = NULL;
>>> + }
>>> +
>>> + vmf.vma = vma;
>>> + vmf.pgoff = linear_page_index(vma, address);
>>> + vmf.gfp_mask = __get_fault_gfp_mask(vma);
>>> + vmf.sequence = seq;
>>> + vmf.flags = flags;
>>> +
>>> + local_irq_enable();
>>> +
>>> + /*
>>> + * We need to re-validate the VMA after checking the bounds, otherwise
>>> + * we might have a false positive on the bounds.
>>> + */
>>> + if (read_seqcount_retry(&vma->vm_sequence, seq))
>>> + goto out_put;
>>> +
>>> + mem_cgroup_oom_enable();
>>> + ret = handle_pte_fault(&vmf);
>>> + mem_cgroup_oom_disable();
>>> +
>>> + put_vma(vma);
>>> +
>>> + /*
>>> + * The task may have entered a memcg OOM situation but
>>> + * if the allocation error was handled gracefully (no
>>> + * VM_FAULT_OOM), there is no need to kill anything.
>>> + * Just clean up the OOM state peacefully.
>>> + */
>>> + if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
>>> + mem_cgroup_oom_synchronize(false);
>>> + return ret;
>>> +
>>> +out_walk:
>>> + local_irq_enable();
>>> +out_put:
>>> + put_vma(vma);
>>> + return ret;
>>> +}
>>> +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
>>> +
>>> /*
>>> * By the time we get here, we already hold the mm semaphore
>>> *
>>
>
> .
>


\
 
 \ /
  Last update: 2018-07-25 11:04    [W:0.114 / U:0.380 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site