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;
--
2.20.1
