Messages in this thread Patch in this message | | | From | Steven Price <> | Subject | Re: [PATCH v16 11/25] mm: pagewalk: Add p4d_entry() and pgd_entry() | Date | Thu, 12 Dec 2019 13:15:25 +0000 |
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On 12/12/2019 11:33, Thomas Hellström (VMware) wrote: > On 12/12/19 12:23 PM, Thomas Hellström (VMware) wrote: >> On 12/6/19 2:53 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. Since there have never >>> been upstream users of this, revert the semantics back to match the >>> other callbacks. This means pud_entry() is called for all entries, not >>> just transparent huge pages.
When I wrote that there were no upstream users, which sadly shows how long ago that was :(
>> Actually, there are two users of pud_entry(), in hmm.c and since >> 5.5rc1 also mapping_dirty_helpers.c. The latter one is unproblematic >> and requires no attention but the one in hmm.c is probably largely >> untested, and seems to assume it was called outside of the spinlock. >> >> The problem with the current patch is that the hmm pud_entry will >> traverse also pmds, so that will be done twice now. >> >> In another thread we were discussing a means of rerunning the level >> (in case of a race), or continuing after a level, based on the return >> value after the callback. The change was fairly invasive, >> > Hmm. Forgot to remove the above text that appears twice. :(. The correct > one is inline below. > >> >>> Tested-by: Zong Li <zong.li@sifive.com> >>> Signed-off-by: Steven Price <steven.price@arm.com> >>> --- >>> include/linux/pagewalk.h | 19 +++++++++++++------ >>> mm/pagewalk.c | 27 ++++++++++++++++----------- >>> 2 files changed, 29 insertions(+), 17 deletions(-) >>> >>> diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h >>> index 6ec82e92c87f..06790f23957f 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, >>> diff --git a/mm/pagewalk.c b/mm/pagewalk.c >>> index ea0b9e606ad1..c089786e7a7f 100644 >>> --- a/mm/pagewalk.c >>> +++ b/mm/pagewalk.c >>> @@ -94,15 +94,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned >>> long addr, unsigned long end, >>> } >>> if (ops->pud_entry) { >>> - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); >>> - >>> - if (ptl) { >>> - err = ops->pud_entry(pud, addr, next, walk); >>> - spin_unlock(ptl); >>> - if (err) >>> - break; >>> - continue; >>> - } >>> + err = ops->pud_entry(pud, addr, next, walk); >>> + if (err) >>> + break; >> >> Actually, there are two current users of pud_entry(), in hmm.c and >> since 5.5rc1 also mapping_dirty_helpers.c. The latter one is >> unproblematic and requires no attention but the one in hmm.c is >> probably largely untested, and seems to assume it was called outside >> of the spinlock.
Thanks for pointing that out, I guess the simplest fix would be to squash in something like the below which should restore the old behaviour for hmm.c without affecting others.
Steve
---8<---- diff --git a/mm/hmm.c b/mm/hmm.c index d379cb6496ae..744b6644d0e4 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -478,19 +478,26 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, pmd_t *pmdp; pud_t pud; int ret; + spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma); + if (!ptl) + return 0; 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 +506,20 @@ 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; } @@ -517,7 +528,8 @@ 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; + ret = 0; + goto out_unlock; } split_huge_pud(walk->vma, pudp, addr); @@ -529,10 +541,14 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, next = pmd_addr_end(addr, end); ret = hmm_vma_walk_pmd(pmdp, addr, next, walk); if (ret) - return ret; + goto out_unlock; } while (pmdp++, addr = next, addr != end); - return 0; + ret = 0; + +out_unlock: + spin_unlock(ptl); + return ret; } #else #define hmm_vma_walk_pud NULL
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