mm/mremap: calculate extent in one place

Page tables is moved on the base of PMD.  This requires both source and
destination range should meet the requirement.

Current code works well since move_huge_pmd() and move_normal_pmd() would
check old_addr and new_addr again.  And then return to move_ptes() if the
either of them is not aligned.

Instead of calculating the extent separately, it is better to calculate in
one place, so we know it is not necessary to try move pmd.  By doing so,
the logic seems a little clear.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Link: http://lkml.kernel.org/r/20200708095028.41706-3-richard.weiyang@linux.alibaba.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mremap.c b/mm/mremap.c
index 4f434062d154030f5ce3a6757b1fe31eb0c7d45e..c3622bfcf6d9b20c661993564fec07c8a42f3606 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -277,6 +277,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
                extent = next - old_addr;
                if (extent > old_end - old_addr)
                        extent = old_end - old_addr;
+               next = (new_addr + PMD_SIZE) & PMD_MASK;
+               if (extent > next - new_addr)
+                       extent = next - new_addr;
                old_pmd = get_old_pmd(vma->vm_mm, old_addr);
                if (!old_pmd)
                        continue;
@@ -320,9 +323,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 
                if (pte_alloc(new_vma->vm_mm, new_pmd))
                        break;
-               next = (new_addr + PMD_SIZE) & PMD_MASK;
-               if (extent > next - new_addr)
-                       extent = next - new_addr;
                move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
                          new_pmd, new_addr, need_rmap_locks);
        }