Commit ac541f25 authored Oct 23, 2019 by Ralph Campbell Committed by Jason Gunthorpe Oct 29, 2019

mm/hmm: allow snapshot of the special zero page

If a device driver like nouveau tries to use hmm_range_fault() to access
the special shared zero page in system memory, hmm_range_fault() will
return -EFAULT and kill the process.

Allow hmm_range_fault() to return success (0) when the CPU pagetable entry
points to the special shared zero page.

page_to_pfn() and pfn_to_page() are defined on the zero page so just
handle it like any other page.

Link: https://lore.kernel.org/r/20191023195515.13168-3-rcampbell@nvidia.com


Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

parent d6d5df1d

mm/hmm.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -532,9 +532,15 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
		if (unlikely(!hmm_vma_walk->pgmap))
		return -EBUSY;
		} else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) {
		if (!is_zero_pfn(pte_pfn(pte))) {
		*pfn = range->values[HMM_PFN_SPECIAL];
		return -EFAULT;
		}
		/*
		* Since each architecture defines a struct page for the zero
		* page, just fall through and treat it like a normal page.
		*/
		}

		*pfn = hmm_device_entry_from_pfn(range, pte_pfn(pte)) \| cpu_flags;
		return 0;

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