| Message ID | 20200311183506.3997-3-jgg@ziepe.ca (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Various error case bug fixes for hmm_range_fault() | expand |
On Mon, Mar 16, 2020 at 10:02:50AM +0100, Christoph Hellwig wrote: > On Wed, Mar 11, 2020 at 03:35:00PM -0300, Jason Gunthorpe wrote: > > @@ -694,6 +672,15 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags) > > return -EBUSY; > > ret = walk_page_range(mm, hmm_vma_walk.last, range->end, > > &hmm_walk_ops, &hmm_vma_walk); > > + /* > > + * A pgmap is kept cached in the hmm_vma_walk to avoid expensive > > + * searching in the probably common case that the pgmap is the > > + * same for the entire requested range. > > + */ > > + if (hmm_vma_walk.pgmap) { > > + put_dev_pagemap(hmm_vma_walk.pgmap); > > + hmm_vma_walk.pgmap = NULL; > > + } > > } while (ret == -EBUSY); > > In which case it should only be put on return, and not for every loop. I chose this to be simple without having to goto unwind it. So, instead like this: @@ -683,21 +661,33 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags) .flags = flags, }; struct mm_struct *mm = range->notifier->mm; - int ret; + long ret; lockdep_assert_held(&mm->mmap_sem); do { /* If range is no longer valid force retry. */ if (mmu_interval_check_retry(range->notifier, - range->notifier_seq)) - return -EBUSY; + range->notifier_seq)) { + ret = -EBUSY; + goto out; + } ret = walk_page_range(mm, hmm_vma_walk.last, range->end, &hmm_walk_ops, &hmm_vma_walk); } while (ret == -EBUSY); if (ret) - return ret; - return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT; + goto out; + ret = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT; + +out: + /* + * A pgmap is kept cached in the hmm_vma_walk to avoid expensive + * searching in the probably common case that the pgmap is the + * same for the entire requested range. + */ + if (hmm_vma_walk.pgmap) + put_dev_pagemap(hmm_vma_walk.pgmap); + return ret; } EXPORT_SYMBOL(hmm_range_fault); ? > I still think the right fix is to just delete all the unused and broken > pgmap handling code. If we ever need to add it back it can be added > in a proper understood and tested way. What I want to add is something like if (pgmap != walk->required_pgmap) cpu_flags = 0 hmm_range_need_fault(..., cpu_flags, ...) Which will fix a bug in nouveau where it blindly assumes any device pages are its own, IIRC. I think Ralph observed it needs to be here, because if the pgmap doesn't match then it should trigger migration, in a single call, rather than iterating. I'm mostly expecting to replace all the other pgmap code, but keep the pgmap caching. The existing pgmap stuff seems approx right, but useless.. Jason
On Mon, Mar 16, 2020 at 07:13:24PM +0100, Christoph Hellwig wrote: > On Mon, Mar 16, 2020 at 03:07:13PM -0300, Jason Gunthorpe wrote: > > I chose this to be simple without having to goto unwind it. > > > > So, instead like this: > > As Ń•aid, and per the previous discussion: I think just removing the > pgmap lookup is the right thing to do here. Something like this patch: OK. I think I get it now. We don't even signal that the pfn is a pgmap to the caller, so the caller must assume the pfn is CPU memory and can be dma mapped. At that point it doesn't matter what kind of pgmap it is. Races here are resolved by notifiers as we can't destroy the pgmap without triggering invalidation of the pte So removing is the right thing to do, and the fixing for the device_private case is closer to the hunk I just sent. Jason
diff --git a/mm/hmm.c b/mm/hmm.c index 35f85424176d14..9e8f68eb83287a 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -239,10 +239,6 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr, } pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags; } - if (hmm_vma_walk->pgmap) { - put_dev_pagemap(hmm_vma_walk->pgmap); - hmm_vma_walk->pgmap = NULL; - } hmm_vma_walk->last = end; return 0; } @@ -360,10 +356,6 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, return 0; fault: - if (hmm_vma_walk->pgmap) { - put_dev_pagemap(hmm_vma_walk->pgmap); - hmm_vma_walk->pgmap = NULL; - } pte_unmap(ptep); /* Fault any virtual address we were asked to fault */ return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk); @@ -446,16 +438,6 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, return r; } } - if (hmm_vma_walk->pgmap) { - /* - * We do put_dev_pagemap() here and not in hmm_vma_handle_pte() - * so that we can leverage get_dev_pagemap() optimization which - * will not re-take a reference on a pgmap if we already have - * one. - */ - put_dev_pagemap(hmm_vma_walk->pgmap); - hmm_vma_walk->pgmap = NULL; - } pte_unmap(ptep - 1); hmm_vma_walk->last = addr; @@ -529,10 +511,6 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags; } - if (hmm_vma_walk->pgmap) { - put_dev_pagemap(hmm_vma_walk->pgmap); - hmm_vma_walk->pgmap = NULL; - } hmm_vma_walk->last = end; goto out_unlock; } @@ -694,6 +672,15 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags) return -EBUSY; ret = walk_page_range(mm, hmm_vma_walk.last, range->end, &hmm_walk_ops, &hmm_vma_walk); + /* + * A pgmap is kept cached in the hmm_vma_walk to avoid expensive + * searching in the probably common case that the pgmap is the + * same for the entire requested range. + */ + if (hmm_vma_walk.pgmap) { + put_dev_pagemap(hmm_vma_walk.pgmap); + hmm_vma_walk.pgmap = NULL; + } } while (ret == -EBUSY); if (ret)