On 23.10.19 21:55, Ralph Campbell wrote:
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. Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx> --- mm/hmm.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index acf7a664b38c..8c96c9ddcae5 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -529,8 +529,14 @@ 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)) { - *pfn = range->values[HMM_PFN_SPECIAL]; - return -EFAULT; + 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;
Acked-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
