mm/hmm: do not unconditionally set pfns when returning EBUSY

In hmm_vma_handle_pte() and hmm_vma_walk_hugetlb_entry() if fault happens
then -EBUSY will be returned and the pfns input flags will have been
destroyed.

For hmm_vma_handle_pte() set HMM_PFN_NONE only on the success returns that
don't otherwise store to pfns.

For hmm_vma_walk_hugetlb_entry() all exit paths already set pfns, so
remove the redundant store.

Fixes: 2aee09d8c116 ("mm/hmm: change hmm_vma_fault() to allow write fault on page basis")
Link: https://lore.kernel.org/r/20200327200021.29372-8-jgg@ziepe.ca
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/mm/hmm.c b/mm/hmm.c
index 53192c32abc93eb45067c4ebba6f3e5d5a8fef0e..660e8db44811fade43b164c6c8afce41c5feb49a 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -250,11 +250,11 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
        pte_t pte = *ptep;
        uint64_t orig_pfn = *pfn;
 
-       *pfn = range->values[HMM_PFN_NONE];
        if (pte_none(pte)) {
                required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0);
                if (required_fault)
                        goto fault;
+               *pfn = range->values[HMM_PFN_NONE];
                return 0;
        }
 
@@ -275,8 +275,10 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
                }
 
                required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0);
-               if (!required_fault)
+               if (!required_fault) {
+                       *pfn = range->values[HMM_PFN_NONE];
                        return 0;
+               }
 
                if (!non_swap_entry(entry))
                        goto fault;
@@ -494,7 +496,6 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 
        i = (start - range->start) >> PAGE_SHIFT;
        orig_pfn = range->pfns[i];
-       range->pfns[i] = range->values[HMM_PFN_NONE];
        cpu_flags = pte_to_hmm_pfn_flags(range, entry);
        required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags);
        if (required_fault) {