"Aneesh Kumar K.V" <aneesh.ku...@linux.ibm.com> writes:
> On 5/20/21 6:16 PM, Peter Xu wrote:
>> On Thu, May 20, 2021 at 01:56:54PM +0530, Aneesh Kumar K.V wrote:
>>>> This seems to work at least for my userfaultfd test on shmem, however I
>>>> don't
>>>> fully understand the commit message [1] on: How do we guarantee we're not
>>>> moving a thp pte?
>>>>
>>>
>>> move_page_tables() checks for pmd_trans_huge() and ends up calling
>>> move_huge_pmd if it is a THP entry.
>>
>> Sorry to be unclear: what if a huge pud thp?
>>
>
> I am still checking. Looking at the code before commit
> c49dd340180260c6239e453263a9a244da9a7c85, I don't see kernel handling
> huge pud thp. I haven't studied huge pud thp enough to understand
> whether c49dd340180260c6239e453263a9a244da9a7c85 intent to add that
> support.
>
> We can do a move_huge_pud() like we do for huge pmd thp. But I am not
> sure whether we handle those VMA's earlier and restrict mremap on them?
something like this? (not even compile tested). I am still not sure
whether this is really needed or we handle DAX VMA's in some other form.
diff --git a/mm/mremap.c b/mm/mremap.c
index 47c255b60150..037a7bd311f1 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -324,10 +324,51 @@ static inline bool move_normal_pud(struct vm_area_struct
*vma,
}
#endif
+
+static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
+ unsigned long new_addr, pud_t *old_pud, pud_t
*new_pud)
+{
+ spinlock_t *old_ptl, *new_ptl;
+ struct mm_struct *mm = vma->vm_mm;
+ pud_t pud;
+
+ /*
+ * The destination pud shouldn't be established, free_pgtables()
+ * should have released it.
+ */
+ if (WARN_ON_ONCE(!pud_none(*new_pud)))
+ return false;
+
+ /*
+ * We don't have to worry about the ordering of src and dst
+ * ptlocks because exclusive mmap_lock prevents deadlock.
+ */
+ old_ptl = pud_lock(vma->vm_mm, old_pud);
+ new_ptl = pud_lockptr(mm, new_pud);
+ if (new_ptl != old_ptl)
+ spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
+
+ /* Clear the pud */
+ pud = *old_pud;
+ pud_clear(old_pud);
+
+ VM_BUG_ON(!pud_none(*new_pud));
+
+ /* Set the new pud */
+ set_pud_at(mm, new_addr, new_pud, pud);
+ flush_pud_tlb_range(vma, old_addr, old_addr + HPAGE_PUD_SIZE);
+ if (new_ptl != old_ptl)
+ spin_unlock(new_ptl);
+ spin_unlock(old_ptl);
+
+ return true;
+}
+
enum pgt_entry {
NORMAL_PMD,
HPAGE_PMD,
NORMAL_PUD,
+ HPAGE_PUD,
};
/*
@@ -347,6 +388,7 @@ static __always_inline unsigned long get_extent(enum
pgt_entry entry,
mask = PMD_MASK;
size = PMD_SIZE;
break;
+ case HPAGE_PUD:
case NORMAL_PUD:
mask = PUD_MASK;
size = PUD_SIZE;
@@ -395,6 +437,12 @@ static bool move_pgt_entry(enum pgt_entry entry, struct
vm_area_struct *vma,
move_huge_pmd(vma, old_addr, new_addr, old_entry,
new_entry);
break;
+ case HPAGE_PUD:
+ moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE_PUD) &&
+ move_huge_pud(vma, old_addr, new_addr, old_entry,
+ new_entry);
+ break;
+
default:
WARN_ON_ONCE(1);
break;
@@ -429,15 +477,23 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
* PUD level if possible.
*/
extent = get_extent(NORMAL_PUD, old_addr, old_end, new_addr);
- if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {
- pud_t *old_pud, *new_pud;
- old_pud = get_old_pud(vma->vm_mm, old_addr);
- if (!old_pud)
+ old_pud = get_old_pud(vma->vm_mm, old_addr);
+ if (!old_pud)
+ continue;
+ new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
+ if (!new_pud)
+ break;
+ if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) {
+ if (extent == HPAGE_PUD_SIZE) {
+ move_pgt_entry(HPAGE_PUD, vma, old_addr,
new_addr,
+ old_pud, new_pud,
need_rmap_locks);
+ /* We ignore and continue on error? */
continue;
- new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
- if (!new_pud)
- break;
+ }
+ } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent ==
PUD_SIZE) {
+ pud_t *old_pud, *new_pud;
+
if (move_pgt_entry(NORMAL_PUD, vma, old_addr, new_addr,
old_pud, new_pud, need_rmap_locks))
continue;
>
> Are huge pud thp only allowed with DAX vmas?
>
>
> -aneesh
