[Qemu-devel] [PATCH 2/7] userfaultfd: propagate the full address in THP faults

[Andrea Arcangeli]

The THP faults were not propagating the original fault address. The latest
version of the API with uffd.arg.pagefault.address is supposed to propagate the
full address through THP faults.

This was not a kernel crashing bug and it wouldn't risk to corrupt
user memory, but it would cause a SIGBUS failure because the wrong page was
being copied.

For various reasons this wasn't easily reproducible in the qemu
workload, but the strestest exposed the problem immediately.

Signed-off-by: Andrea Arcangeli <address@hidden>
---
 mm/huge_memory.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 80d4ae1..73eb404 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -717,13 +717,14 @@ static inline pmd_t mk_huge_pmd(struct page *page, 
pgprot_t prot)
 
 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
                                        struct vm_area_struct *vma,
-                                       unsigned long haddr, pmd_t *pmd,
+                                       unsigned long address, pmd_t *pmd,
                                        struct page *page, gfp_t gfp,
                                        unsigned int flags)
 {
        struct mem_cgroup *memcg;
        pgtable_t pgtable;
        spinlock_t *ptl;
+       unsigned long haddr = address & HPAGE_PMD_MASK;
 
        VM_BUG_ON_PAGE(!PageCompound(page), page);
 
@@ -765,7 +766,7 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct 
*mm,
                        mem_cgroup_cancel_charge(page, memcg);
                        put_page(page);
                        pte_free(mm, pgtable);
-                       ret = handle_userfault(vma, haddr, flags,
+                       ret = handle_userfault(vma, address, flags,
                                               VM_UFFD_MISSING);
                        VM_BUG_ON(ret & VM_FAULT_FALLBACK);
                        return ret;
@@ -841,7 +842,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct 
vm_area_struct *vma,
                if (pmd_none(*pmd)) {
                        if (userfaultfd_missing(vma)) {
                                spin_unlock(ptl);
-                               ret = handle_userfault(vma, haddr, flags,
+                               ret = handle_userfault(vma, address, flags,
                                                       VM_UFFD_MISSING);
                                VM_BUG_ON(ret & VM_FAULT_FALLBACK);
                        } else {
@@ -865,7 +866,8 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct 
vm_area_struct *vma,
                count_vm_event(THP_FAULT_FALLBACK);
                return VM_FAULT_FALLBACK;
        }
-       return __do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page, gfp, 
flags);
+       return __do_huge_pmd_anonymous_page(mm, vma, address, pmd, page, gfp,
+                                           flags);
 }
 
 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,