Commit ac541f25 authored by Ralph Campbell's avatar Ralph Campbell Committed by Jason Gunthorpe

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.comSigned-off-by: default avatarRalph Campbell <rcampbell@nvidia.com>
Reviewed-by: default avatar"Jérôme Glisse" <jglisse@redhat.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
parent d6d5df1d
......@@ -532,8 +532,14 @@ 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;
......
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