Commit 068354ad authored by Jason Gunthorpe's avatar Jason Gunthorpe
Browse files

mm/hmm: remove pgmap checking for devmap pages 

The checking boils down to some racy check if the pagemap is still
available or not. Instead of checking this, rely entirely on the
notifiers, if a pagemap is destroyed then all pages that belong to it must
be removed from the tables and the notifiers triggered.

Link: https://lore.kernel.org/r/20200327200021.29372-2-jgg@ziepe.ca


Reviewed-by: default avatarRalph Campbell <rcampbell@nvidia.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Tested-by: default avatarRalph Campbell <rcampbell@nvidia.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
parent 08ddddda

mm/hmm.c

+2 −48
Original line number Diff line number Diff line
@@ -28,7 +28,6 @@ 


struct hmm_vma_walk {

	struct hmm_range	*range;

	struct dev_pagemap	*pgmap;

	unsigned long		last;

	unsigned int		flags;

};
@@ -196,19 +195,8 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr, 
		return hmm_vma_fault(addr, end, fault, write_fault, walk);



	pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);

	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {

		if (pmd_devmap(pmd)) {

			hmm_vma_walk->pgmap = get_dev_pagemap(pfn,

					      hmm_vma_walk->pgmap);

			if (unlikely(!hmm_vma_walk->pgmap))

				return -EBUSY;

		}

	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)

		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;

}
@@ -300,15 +288,6 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, 
	if (fault || write_fault)

		goto fault;



	if (pte_devmap(pte)) {

		hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte),

					      hmm_vma_walk->pgmap);

		if (unlikely(!hmm_vma_walk->pgmap)) {

			pte_unmap(ptep);

			return -EBUSY;

		}

	}



	/*

	 * Since each architecture defines a struct page for the zero page, just

	 * fall through and treat it like a normal page.
@@ -328,10 +307,6 @@ 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_fault(addr, end, fault, write_fault, walk);
@@ -418,16 +393,6 @@ 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;
@@ -491,20 +456,9 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, 
		}



		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)) {

				ret = -EBUSY;

				goto out_unlock;

			}

		for (i = 0; i < npages; ++i, ++pfn)

			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;

	}