| Message ID | 20191218162402.45610-12-steven.price@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Generic page walk and ptdump | expand |
Hi, Steven, On 12/18/19 5:23 PM, Steven Price wrote: > pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 > ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were > no users. We're about to add users so reintroduce them, along with > p4d_entry() as we now have 5 levels of tables. > > Note that commit a00cc7d9dd93d66a ("mm, x86: add support for > PUD-sized transparent hugepages") already re-added pud_entry() but with > different semantics to the other callbacks. This commit reverts the > semantics back to match the other callbacks. > > To support hmm.c which now uses the new semantics of pud_entry() a new > member ('action') of struct mm_walk is added which allows the callbacks > to either descend (ACTION_SUBTREE, the default), skip (ACTION_CONTINUE) > or repeat the callback (ACTION_AGAIN). hmm.c is then updated to call > pud_trans_huge_lock() itself and make use of the splitting/retry logic > of the core code. > > After this change pud_entry() is called for all entries, not just > transparent huge pages. > > Signed-off-by: Steven Price <steven.price@arm.com> I have a couple of comments that are actually mostly related to pre-existing bugs, but that affect code that are touched by this patch. Perhaps this is most cleanly addressed by a follow-up patch. Up to you to decide. Since these problems are pre-existing, Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com> Thanks, Thomas > --- > include/linux/pagewalk.h | 34 ++++++++++++++++++++----- > mm/hmm.c | 55 ++++++++++++++++++++++------------------ > mm/pagewalk.c | 50 +++++++++++++++++++++++++----------- > 3 files changed, 94 insertions(+), 45 deletions(-) > > diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h > index 6ec82e92c87f..aa6a0b63964e 100644 > --- a/include/linux/pagewalk.h > +++ b/include/linux/pagewalk.h > @@ -8,15 +8,15 @@ struct mm_walk; > > /** > * mm_walk_ops - callbacks for walk_page_range > - * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry > - * this handler should only handle pud_trans_huge() puds. > - * the pmd_entry or pte_entry callbacks will be used for > - * regular PUDs. > - * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry > + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry > + * @p4d_entry: if set, called for each non-empty P4D entry > + * @pud_entry: if set, called for each non-empty PUD entry > + * @pmd_entry: if set, called for each non-empty PMD entry > * this handler is required to be able to handle > * pmd_trans_huge() pmds. They may simply choose to > * split_huge_page() instead of handling it explicitly. > - * @pte_entry: if set, called for each non-empty PTE (4th-level) entry > + * @pte_entry: if set, called for each non-empty PTE (lowest-level) > + * entry > * @pte_hole: if set, called for each hole at all levels > * @hugetlb_entry: if set, called for each hugetlb entry > * @test_walk: caller specific callback function to determine whether > @@ -27,8 +27,15 @@ struct mm_walk; > * @pre_vma: if set, called before starting walk on a non-null vma. > * @post_vma: if set, called after a walk on a non-null vma, provided > * that @pre_vma and the vma walk succeeded. > + * > + * p?d_entry callbacks are called even if those levels are folded on a > + * particular architecture/configuration. > */ > struct mm_walk_ops { > + int (*pgd_entry)(pgd_t *pgd, unsigned long addr, > + unsigned long next, struct mm_walk *walk); > + int (*p4d_entry)(p4d_t *p4d, unsigned long addr, > + unsigned long next, struct mm_walk *walk); > int (*pud_entry)(pud_t *pud, unsigned long addr, > unsigned long next, struct mm_walk *walk); > int (*pmd_entry)(pmd_t *pmd, unsigned long addr, > @@ -47,11 +54,25 @@ struct mm_walk_ops { > void (*post_vma)(struct mm_walk *walk); > }; > > +/* > + * Action for pud_entry / pmd_entry callbacks. > + * ACTION_SUBTREE is the default > + */ > +enum page_walk_action { > + /* Descend to next level, splitting huge pages if needed and possible */ > + ACTION_SUBTREE = 0, > + /* Continue to next entry at this level (ignoring any subtree) */ > + ACTION_CONTINUE = 1, > + /* Call again for this entry */ > + ACTION_AGAIN = 2 > +}; > + > /** > * mm_walk - walk_page_range data > * @ops: operation to call during the walk > * @mm: mm_struct representing the target process of page table walk > * @vma: vma currently walked (NULL if walking outside vmas) > + * @action: next action to perform (see enum page_walk_action) > * @private: private data for callbacks' usage > * > * (see the comment on walk_page_range() for more details) > @@ -60,6 +81,7 @@ struct mm_walk { > const struct mm_walk_ops *ops; > struct mm_struct *mm; > struct vm_area_struct *vma; > + enum page_walk_action action; > void *private; > }; > > diff --git a/mm/hmm.c b/mm/hmm.c > index d379cb6496ae..05241c82e05c 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -477,20 +477,30 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > unsigned long addr = start, next; > pmd_t *pmdp; > pud_t pud; > - int ret; > + int ret = 0; > + spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma); > + > + if (!ptl) > + return 0; Since if we didn't get the PTL here, the pud might be unstable in which case we want to retry: if (!ptl) { if (pud_trans_unstable(pudp)) walk->action = ACTION_AGAIN; return 0; } > + > + /* Normally we don't want to split the huge page */ > + walk->action = ACTION_CONTINUE; > > -again: > pud = READ_ONCE(*pudp); We have the lock now, so READ_ONCE could probably be a simple dereference. > - if (pud_none(pud)) > - return hmm_vma_walk_hole(start, end, walk); > + if (pud_none(pud)) { > + ret = hmm_vma_walk_hole(start, end, walk); > + goto out_unlock; > + } pud_trans_huge_lock() successful return means pud_none() is always false. > > if (pud_huge(pud) && pud_devmap(pud)) { > unsigned long i, npages, pfn; > uint64_t *pfns, cpu_flags; > bool fault, write_fault; > > - if (!pud_present(pud)) > - return hmm_vma_walk_hole(start, end, walk); > + if (!pud_present(pud)) { > + ret = hmm_vma_walk_hole(start, end, walk); > + goto out_unlock; > + } Can't see !pud_present happening either after a succesful pud_trans_huge_lock(). > > i = (addr - range->start) >> PAGE_SHIFT; > npages = (end - addr) >> PAGE_SHIFT; > @@ -499,16 +509,20 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > cpu_flags = pud_to_hmm_pfn_flags(range, pud); > hmm_range_need_fault(hmm_vma_walk, pfns, npages, > cpu_flags, &fault, &write_fault); > - if (fault || write_fault) > - return hmm_vma_walk_hole_(addr, end, fault, > - write_fault, walk); > + if (fault || write_fault) { > + ret = hmm_vma_walk_hole_(addr, end, fault, > + write_fault, walk); > + goto out_unlock; > + } > > pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > for (i = 0; i < npages; ++i, ++pfn) { > hmm_vma_walk->pgmap = get_dev_pagemap(pfn, > hmm_vma_walk->pgmap); > - if (unlikely(!hmm_vma_walk->pgmap)) > - return -EBUSY; > + if (unlikely(!hmm_vma_walk->pgmap)) { > + ret = -EBUSY; > + goto out_unlock; > + } > pfns[i] = hmm_device_entry_from_pfn(range, pfn) | > cpu_flags; > } > @@ -517,22 +531,15 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > hmm_vma_walk->pgmap = NULL; > } > hmm_vma_walk->last = end; > - return 0; > + goto out_unlock; > } > > - split_huge_pud(walk->vma, pudp, addr); > - if (pud_none(*pudp)) > - goto again; > + /* Ask for the PUD to be split */ > + walk->action = ACTION_SUBTREE; > > - pmdp = pmd_offset(pudp, addr); > - do { > - next = pmd_addr_end(addr, end); > - ret = hmm_vma_walk_pmd(pmdp, addr, next, walk); > - if (ret) > - return ret; > - } while (pmdp++, addr = next, addr != end); > - > - return 0; > +out_unlock: > + spin_unlock(ptl); > + return ret; > } > #else > #define hmm_vma_walk_pud NULL > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index ea0b9e606ad1..690af44609e2 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -46,6 +46,9 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > break; > continue; > } > + > + walk->action = ACTION_SUBTREE; > + > /* > * This implies that each ->pmd_entry() handler > * needs to know about pmd_trans_huge() pmds > @@ -55,16 +58,21 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > if (err) > break; > > + if (walk->action == ACTION_AGAIN) > + goto again; > + > /* > * Check this here so we only break down trans_huge > * pages when we _need_ to > */ > - if (!ops->pte_entry) > + if (walk->action == ACTION_CONTINUE || > + !(ops->pte_entry)) > continue; > > split_huge_pmd(walk->vma, pmd, addr); > if (pmd_trans_unstable(pmd)) > goto again; > + > err = walk_pte_range(pmd, addr, next, walk); > if (err) > break; > @@ -93,24 +101,25 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > continue; > } > > - if (ops->pud_entry) { > - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); > + walk->action = ACTION_SUBTREE; > > - if (ptl) { > - err = ops->pud_entry(pud, addr, next, walk); > - spin_unlock(ptl); > - if (err) > - break; > - continue; > - } > - } > + if (ops->pud_entry) > + err = ops->pud_entry(pud, addr, next, walk); > + if (err) > + break; > + > + if (walk->action == ACTION_AGAIN) > + goto again; > + > + if (walk->action == ACTION_CONTINUE || > + !(ops->pmd_entry || ops->pte_entry)) > + continue; > > split_huge_pud(walk->vma, pud, addr); > if (pud_none(*pud)) Here we should really have if (pud_trans_unstable(pud)) Thanks, Thomas
On 19/12/2019 14:25, Thomas Hellström (VMware) wrote: > Hi, Steven, > > > On 12/18/19 5:23 PM, Steven Price wrote: >> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 >> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were >> no users. We're about to add users so reintroduce them, along with >> p4d_entry() as we now have 5 levels of tables. >> >> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for >> PUD-sized transparent hugepages") already re-added pud_entry() but with >> different semantics to the other callbacks. This commit reverts the >> semantics back to match the other callbacks. >> >> To support hmm.c which now uses the new semantics of pud_entry() a new >> member ('action') of struct mm_walk is added which allows the callbacks >> to either descend (ACTION_SUBTREE, the default), skip (ACTION_CONTINUE) >> or repeat the callback (ACTION_AGAIN). hmm.c is then updated to call >> pud_trans_huge_lock() itself and make use of the splitting/retry logic >> of the core code. >> >> After this change pud_entry() is called for all entries, not just >> transparent huge pages. >> >> Signed-off-by: Steven Price <steven.price@arm.com> > > I have a couple of comments that are actually mostly related to > pre-existing bugs, but that affect code that are touched by this patch. > > Perhaps this is most cleanly addressed by a follow-up patch. Up to you > to decide. > > Since these problems are pre-existing, > > Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com> Thanks, I'll send out an extra patch with these changes. Steve > Thanks, > > Thomas > > >> --- >> include/linux/pagewalk.h | 34 ++++++++++++++++++++----- >> mm/hmm.c | 55 ++++++++++++++++++++++------------------ >> mm/pagewalk.c | 50 +++++++++++++++++++++++++----------- >> 3 files changed, 94 insertions(+), 45 deletions(-) >> >> diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h >> index 6ec82e92c87f..aa6a0b63964e 100644 >> --- a/include/linux/pagewalk.h >> +++ b/include/linux/pagewalk.h >> @@ -8,15 +8,15 @@ struct mm_walk; >> /** >> * mm_walk_ops - callbacks for walk_page_range >> - * @pud_entry: if set, called for each non-empty PUD >> (2nd-level) entry >> - * this handler should only handle pud_trans_huge() puds. >> - * the pmd_entry or pte_entry callbacks will be used for >> - * regular PUDs. >> - * @pmd_entry: if set, called for each non-empty PMD >> (3rd-level) entry >> + * @pgd_entry: if set, called for each non-empty PGD >> (top-level) entry >> + * @p4d_entry: if set, called for each non-empty P4D entry >> + * @pud_entry: if set, called for each non-empty PUD entry >> + * @pmd_entry: if set, called for each non-empty PMD entry >> * this handler is required to be able to handle >> * pmd_trans_huge() pmds. They may simply choose to >> * split_huge_page() instead of handling it explicitly. >> - * @pte_entry: if set, called for each non-empty PTE >> (4th-level) entry >> + * @pte_entry: if set, called for each non-empty PTE >> (lowest-level) >> + * entry >> * @pte_hole: if set, called for each hole at all levels >> * @hugetlb_entry: if set, called for each hugetlb entry >> * @test_walk: caller specific callback function to determine >> whether >> @@ -27,8 +27,15 @@ struct mm_walk; >> * @pre_vma: if set, called before starting walk on a >> non-null vma. >> * @post_vma: if set, called after a walk on a non-null >> vma, provided >> * that @pre_vma and the vma walk succeeded. >> + * >> + * p?d_entry callbacks are called even if those levels are folded on a >> + * particular architecture/configuration. >> */ >> struct mm_walk_ops { >> + int (*pgd_entry)(pgd_t *pgd, unsigned long addr, >> + unsigned long next, struct mm_walk *walk); >> + int (*p4d_entry)(p4d_t *p4d, unsigned long addr, >> + unsigned long next, struct mm_walk *walk); >> int (*pud_entry)(pud_t *pud, unsigned long addr, >> unsigned long next, struct mm_walk *walk); >> int (*pmd_entry)(pmd_t *pmd, unsigned long addr, >> @@ -47,11 +54,25 @@ struct mm_walk_ops { >> void (*post_vma)(struct mm_walk *walk); >> }; >> +/* >> + * Action for pud_entry / pmd_entry callbacks. >> + * ACTION_SUBTREE is the default >> + */ >> +enum page_walk_action { >> + /* Descend to next level, splitting huge pages if needed and >> possible */ >> + ACTION_SUBTREE = 0, >> + /* Continue to next entry at this level (ignoring any subtree) */ >> + ACTION_CONTINUE = 1, >> + /* Call again for this entry */ >> + ACTION_AGAIN = 2 >> +}; >> + >> /** >> * mm_walk - walk_page_range data >> * @ops: operation to call during the walk >> * @mm: mm_struct representing the target process of page >> table walk >> * @vma: vma currently walked (NULL if walking outside vmas) >> + * @action: next action to perform (see enum page_walk_action) >> * @private: private data for callbacks' usage >> * >> * (see the comment on walk_page_range() for more details) >> @@ -60,6 +81,7 @@ struct mm_walk { >> const struct mm_walk_ops *ops; >> struct mm_struct *mm; >> struct vm_area_struct *vma; >> + enum page_walk_action action; >> void *private; >> }; >> diff --git a/mm/hmm.c b/mm/hmm.c >> index d379cb6496ae..05241c82e05c 100644 >> --- a/mm/hmm.c >> +++ b/mm/hmm.c >> @@ -477,20 +477,30 @@ static int hmm_vma_walk_pud(pud_t *pudp, >> unsigned long start, unsigned long end, >> unsigned long addr = start, next; >> pmd_t *pmdp; >> pud_t pud; >> - int ret; >> + int ret = 0; >> + spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma); >> + >> + if (!ptl) >> + return 0; > > Since if we didn't get the PTL here, the pud might be unstable in which > case we want to retry: > > if (!ptl) { > if (pud_trans_unstable(pudp)) > walk->action = ACTION_AGAIN; > return 0; > } > > >> + >> + /* Normally we don't want to split the huge page */ >> + walk->action = ACTION_CONTINUE; >> -again: >> pud = READ_ONCE(*pudp); > > We have the lock now, so READ_ONCE could probably be a simple dereference. > >> - if (pud_none(pud)) >> - return hmm_vma_walk_hole(start, end, walk); >> + if (pud_none(pud)) { >> + ret = hmm_vma_walk_hole(start, end, walk); >> + goto out_unlock; >> + } > > pud_trans_huge_lock() successful return means pud_none() is always false. > > >> if (pud_huge(pud) && pud_devmap(pud)) { >> unsigned long i, npages, pfn; >> uint64_t *pfns, cpu_flags; >> bool fault, write_fault; >> - if (!pud_present(pud)) >> - return hmm_vma_walk_hole(start, end, walk); >> + if (!pud_present(pud)) { >> + ret = hmm_vma_walk_hole(start, end, walk); >> + goto out_unlock; >> + } > > Can't see !pud_present happening either after a succesful > pud_trans_huge_lock(). > >> i = (addr - range->start) >> PAGE_SHIFT; >> npages = (end - addr) >> PAGE_SHIFT; >> @@ -499,16 +509,20 @@ static int hmm_vma_walk_pud(pud_t *pudp, >> unsigned long start, unsigned long end, >> cpu_flags = pud_to_hmm_pfn_flags(range, pud); >> hmm_range_need_fault(hmm_vma_walk, pfns, npages, >> cpu_flags, &fault, &write_fault); >> - if (fault || write_fault) >> - return hmm_vma_walk_hole_(addr, end, fault, >> - write_fault, walk); >> + if (fault || write_fault) { >> + ret = hmm_vma_walk_hole_(addr, end, fault, >> + write_fault, walk); >> + goto out_unlock; >> + } >> pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); >> for (i = 0; i < npages; ++i, ++pfn) { >> hmm_vma_walk->pgmap = get_dev_pagemap(pfn, >> hmm_vma_walk->pgmap); >> - if (unlikely(!hmm_vma_walk->pgmap)) >> - return -EBUSY; >> + if (unlikely(!hmm_vma_walk->pgmap)) { >> + ret = -EBUSY; >> + goto out_unlock; >> + } >> pfns[i] = hmm_device_entry_from_pfn(range, pfn) | >> cpu_flags; >> } >> @@ -517,22 +531,15 @@ static int hmm_vma_walk_pud(pud_t *pudp, >> unsigned long start, unsigned long end, >> hmm_vma_walk->pgmap = NULL; >> } >> hmm_vma_walk->last = end; >> - return 0; >> + goto out_unlock; >> } >> - split_huge_pud(walk->vma, pudp, addr); >> - if (pud_none(*pudp)) >> - goto again; >> + /* Ask for the PUD to be split */ >> + walk->action = ACTION_SUBTREE; >> - pmdp = pmd_offset(pudp, addr); >> - do { >> - next = pmd_addr_end(addr, end); >> - ret = hmm_vma_walk_pmd(pmdp, addr, next, walk); >> - if (ret) >> - return ret; >> - } while (pmdp++, addr = next, addr != end); >> - >> - return 0; >> +out_unlock: >> + spin_unlock(ptl); >> + return ret; >> } >> #else >> #define hmm_vma_walk_pud NULL >> diff --git a/mm/pagewalk.c b/mm/pagewalk.c >> index ea0b9e606ad1..690af44609e2 100644 >> --- a/mm/pagewalk.c >> +++ b/mm/pagewalk.c >> @@ -46,6 +46,9 @@ static int walk_pmd_range(pud_t *pud, unsigned long >> addr, unsigned long end, >> break; >> continue; >> } >> + >> + walk->action = ACTION_SUBTREE; >> + >> /* >> * This implies that each ->pmd_entry() handler >> * needs to know about pmd_trans_huge() pmds >> @@ -55,16 +58,21 @@ static int walk_pmd_range(pud_t *pud, unsigned >> long addr, unsigned long end, >> if (err) >> break; >> + if (walk->action == ACTION_AGAIN) >> + goto again; >> + >> /* >> * Check this here so we only break down trans_huge >> * pages when we _need_ to >> */ >> - if (!ops->pte_entry) >> + if (walk->action == ACTION_CONTINUE || >> + !(ops->pte_entry)) >> continue; >> split_huge_pmd(walk->vma, pmd, addr); >> if (pmd_trans_unstable(pmd)) >> goto again; >> + >> err = walk_pte_range(pmd, addr, next, walk); >> if (err) >> break; >> @@ -93,24 +101,25 @@ static int walk_pud_range(p4d_t *p4d, unsigned >> long addr, unsigned long end, >> continue; >> } >> - if (ops->pud_entry) { >> - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); >> + walk->action = ACTION_SUBTREE; >> - if (ptl) { >> - err = ops->pud_entry(pud, addr, next, walk); >> - spin_unlock(ptl); >> - if (err) >> - break; >> - continue; >> - } >> - } >> + if (ops->pud_entry) >> + err = ops->pud_entry(pud, addr, next, walk); >> + if (err) >> + break; >> + >> + if (walk->action == ACTION_AGAIN) >> + goto again; >> + >> + if (walk->action == ACTION_CONTINUE || >> + !(ops->pmd_entry || ops->pte_entry)) >> + continue; >> split_huge_pud(walk->vma, pud, addr); >> if (pud_none(*pud)) > > Here we should really have > > if (pud_trans_unstable(pud)) > > Thanks, > > Thomas > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h index 6ec82e92c87f..aa6a0b63964e 100644 --- a/include/linux/pagewalk.h +++ b/include/linux/pagewalk.h @@ -8,15 +8,15 @@ struct mm_walk; /** * mm_walk_ops - callbacks for walk_page_range - * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry - * this handler should only handle pud_trans_huge() puds. - * the pmd_entry or pte_entry callbacks will be used for - * regular PUDs. - * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry + * @p4d_entry: if set, called for each non-empty P4D entry + * @pud_entry: if set, called for each non-empty PUD entry + * @pmd_entry: if set, called for each non-empty PMD entry * this handler is required to be able to handle * pmd_trans_huge() pmds. They may simply choose to * split_huge_page() instead of handling it explicitly. - * @pte_entry: if set, called for each non-empty PTE (4th-level) entry + * @pte_entry: if set, called for each non-empty PTE (lowest-level) + * entry * @pte_hole: if set, called for each hole at all levels * @hugetlb_entry: if set, called for each hugetlb entry * @test_walk: caller specific callback function to determine whether @@ -27,8 +27,15 @@ struct mm_walk; * @pre_vma: if set, called before starting walk on a non-null vma. * @post_vma: if set, called after a walk on a non-null vma, provided * that @pre_vma and the vma walk succeeded. + * + * p?d_entry callbacks are called even if those levels are folded on a + * particular architecture/configuration. */ struct mm_walk_ops { + int (*pgd_entry)(pgd_t *pgd, unsigned long addr, + unsigned long next, struct mm_walk *walk); + int (*p4d_entry)(p4d_t *p4d, unsigned long addr, + unsigned long next, struct mm_walk *walk); int (*pud_entry)(pud_t *pud, unsigned long addr, unsigned long next, struct mm_walk *walk); int (*pmd_entry)(pmd_t *pmd, unsigned long addr, @@ -47,11 +54,25 @@ struct mm_walk_ops { void (*post_vma)(struct mm_walk *walk); }; +/* + * Action for pud_entry / pmd_entry callbacks. + * ACTION_SUBTREE is the default + */ +enum page_walk_action { + /* Descend to next level, splitting huge pages if needed and possible */ + ACTION_SUBTREE = 0, + /* Continue to next entry at this level (ignoring any subtree) */ + ACTION_CONTINUE = 1, + /* Call again for this entry */ + ACTION_AGAIN = 2 +}; + /** * mm_walk - walk_page_range data * @ops: operation to call during the walk * @mm: mm_struct representing the target process of page table walk * @vma: vma currently walked (NULL if walking outside vmas) + * @action: next action to perform (see enum page_walk_action) * @private: private data for callbacks' usage * * (see the comment on walk_page_range() for more details) @@ -60,6 +81,7 @@ struct mm_walk { const struct mm_walk_ops *ops; struct mm_struct *mm; struct vm_area_struct *vma; + enum page_walk_action action; void *private; }; diff --git a/mm/hmm.c b/mm/hmm.c index d379cb6496ae..05241c82e05c 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -477,20 +477,30 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, unsigned long addr = start, next; pmd_t *pmdp; pud_t pud; - int ret; + int ret = 0; + spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma); + + if (!ptl) + return 0; + + /* Normally we don't want to split the huge page */ + walk->action = ACTION_CONTINUE; -again: pud = READ_ONCE(*pudp); - if (pud_none(pud)) - return hmm_vma_walk_hole(start, end, walk); + if (pud_none(pud)) { + ret = hmm_vma_walk_hole(start, end, walk); + goto out_unlock; + } if (pud_huge(pud) && pud_devmap(pud)) { unsigned long i, npages, pfn; uint64_t *pfns, cpu_flags; bool fault, write_fault; - if (!pud_present(pud)) - return hmm_vma_walk_hole(start, end, walk); + if (!pud_present(pud)) { + ret = hmm_vma_walk_hole(start, end, walk); + goto out_unlock; + } i = (addr - range->start) >> PAGE_SHIFT; npages = (end - addr) >> PAGE_SHIFT; @@ -499,16 +509,20 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, cpu_flags = pud_to_hmm_pfn_flags(range, pud); hmm_range_need_fault(hmm_vma_walk, pfns, npages, cpu_flags, &fault, &write_fault); - if (fault || write_fault) - return hmm_vma_walk_hole_(addr, end, fault, - write_fault, walk); + if (fault || write_fault) { + ret = hmm_vma_walk_hole_(addr, end, fault, + write_fault, walk); + goto out_unlock; + } pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); for (i = 0; i < npages; ++i, ++pfn) { hmm_vma_walk->pgmap = get_dev_pagemap(pfn, hmm_vma_walk->pgmap); - if (unlikely(!hmm_vma_walk->pgmap)) - return -EBUSY; + if (unlikely(!hmm_vma_walk->pgmap)) { + ret = -EBUSY; + goto out_unlock; + } pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags; } @@ -517,22 +531,15 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, hmm_vma_walk->pgmap = NULL; } hmm_vma_walk->last = end; - return 0; + goto out_unlock; } - split_huge_pud(walk->vma, pudp, addr); - if (pud_none(*pudp)) - goto again; + /* Ask for the PUD to be split */ + walk->action = ACTION_SUBTREE; - pmdp = pmd_offset(pudp, addr); - do { - next = pmd_addr_end(addr, end); - ret = hmm_vma_walk_pmd(pmdp, addr, next, walk); - if (ret) - return ret; - } while (pmdp++, addr = next, addr != end); - - return 0; +out_unlock: + spin_unlock(ptl); + return ret; } #else #define hmm_vma_walk_pud NULL diff --git a/mm/pagewalk.c b/mm/pagewalk.c index ea0b9e606ad1..690af44609e2 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -46,6 +46,9 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, break; continue; } + + walk->action = ACTION_SUBTREE; + /* * This implies that each ->pmd_entry() handler * needs to know about pmd_trans_huge() pmds @@ -55,16 +58,21 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, if (err) break; + if (walk->action == ACTION_AGAIN) + goto again; + /* * Check this here so we only break down trans_huge * pages when we _need_ to */ - if (!ops->pte_entry) + if (walk->action == ACTION_CONTINUE || + !(ops->pte_entry)) continue; split_huge_pmd(walk->vma, pmd, addr); if (pmd_trans_unstable(pmd)) goto again; + err = walk_pte_range(pmd, addr, next, walk); if (err) break; @@ -93,24 +101,25 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, continue; } - if (ops->pud_entry) { - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); + walk->action = ACTION_SUBTREE; - if (ptl) { - err = ops->pud_entry(pud, addr, next, walk); - spin_unlock(ptl); - if (err) - break; - continue; - } - } + if (ops->pud_entry) + err = ops->pud_entry(pud, addr, next, walk); + if (err) + break; + + if (walk->action == ACTION_AGAIN) + goto again; + + if (walk->action == ACTION_CONTINUE || + !(ops->pmd_entry || ops->pte_entry)) + continue; split_huge_pud(walk->vma, pud, addr); if (pud_none(*pud)) goto again; - if (ops->pmd_entry || ops->pte_entry) - err = walk_pmd_range(pud, addr, next, walk); + err = walk_pmd_range(pud, addr, next, walk); if (err) break; } while (pud++, addr = next, addr != end); @@ -136,7 +145,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end, break; continue; } - if (ops->pmd_entry || ops->pte_entry) + if (ops->p4d_entry) { + err = ops->p4d_entry(p4d, addr, next, walk); + if (err) + break; + } + if (ops->pud_entry || ops->pmd_entry || ops->pte_entry) err = walk_pud_range(p4d, addr, next, walk); if (err) break; @@ -163,7 +177,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end, break; continue; } - if (ops->pmd_entry || ops->pte_entry) + if (ops->pgd_entry) { + err = ops->pgd_entry(pgd, addr, next, walk); + if (err) + break; + } + if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry || + ops->pte_entry) err = walk_p4d_range(pgd, addr, next, walk); if (err) break;
pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were no users. We're about to add users so reintroduce them, along with p4d_entry() as we now have 5 levels of tables. Note that commit a00cc7d9dd93d66a ("mm, x86: add support for PUD-sized transparent hugepages") already re-added pud_entry() but with different semantics to the other callbacks. This commit reverts the semantics back to match the other callbacks. To support hmm.c which now uses the new semantics of pud_entry() a new member ('action') of struct mm_walk is added which allows the callbacks to either descend (ACTION_SUBTREE, the default), skip (ACTION_CONTINUE) or repeat the callback (ACTION_AGAIN). hmm.c is then updated to call pud_trans_huge_lock() itself and make use of the splitting/retry logic of the core code. After this change pud_entry() is called for all entries, not just transparent huge pages. Signed-off-by: Steven Price <steven.price@arm.com> --- include/linux/pagewalk.h | 34 ++++++++++++++++++++----- mm/hmm.c | 55 ++++++++++++++++++++++------------------ mm/pagewalk.c | 50 +++++++++++++++++++++++++----------- 3 files changed, 94 insertions(+), 45 deletions(-)