On 05.04.23 17:43, Peter Xu wrote:
On Wed, Apr 05, 2023 at 05:17:31PM +0200, David Hildenbrand wrote:
On 05.04.23 17:12, Peter Xu wrote:
On Wed, Apr 05, 2023 at 04:25:34PM +0200, David Hildenbrand wrote:
Looks like what we fixed for hugetlb in commit 44f86392bdd1 ("mm/hugetlb:
fix uffd-wp handling for migration entries in hugetlb_change_protection()")
similarly applies to THP.
Setting/clearing uffd-wp on THP migration entries is not implemented
properly. Further, while removing migration PMDs considers the uffd-wp
bit, inserting migration PMDs does not consider the uffd-wp bit.
We have to set/clear independently of the migration entry type in
change_huge_pmd() and properly copy the uffd-wp bit in
set_pmd_migration_entry().
Verified using a simple reproducer that triggers migration of a THP, that
the set_pmd_migration_entry() no longer loses the uffd-wp bit.
Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Thanks, one trivial nitpick:
---
mm/huge_memory.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 032fb0ef9cd1..bdda4f426d58 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
if (is_swap_pmd(*pmd)) {
swp_entry_t entry = pmd_to_swp_entry(*pmd);
struct page *page = pfn_swap_entry_to_page(entry);
+ pmd_t newpmd;
VM_BUG_ON(!is_pmd_migration_entry(*pmd));
if (is_writable_migration_entry(entry)) {
- pmd_t newpmd;
/*
* A protection check is difficult so
* just be safe and disable write
@@ -1855,8 +1855,16 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
newpmd = pmd_swp_mksoft_dirty(newpmd);
if (pmd_swp_uffd_wp(*pmd))
newpmd = pmd_swp_mkuffd_wp(newpmd);
- set_pmd_at(mm, addr, pmd, newpmd);
+ } else {
+ newpmd = *pmd;
}
+
+ if (uffd_wp)
+ newpmd = pmd_swp_mkuffd_wp(newpmd);
+ else if (uffd_wp_resolve)
+ newpmd = pmd_swp_clear_uffd_wp(newpmd);
+ if (!pmd_same(*pmd, newpmd))
+ set_pmd_at(mm, addr, pmd, newpmd);
goto unlock;
}
#endif
@@ -3251,6 +3259,8 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
pmdswp = swp_entry_to_pmd(entry);
if (pmd_soft_dirty(pmdval))
pmdswp = pmd_swp_mksoft_dirty(pmdswp);
+ if (pmd_swp_uffd_wp(*pvmw->pmd))
+ pmdswp = pmd_swp_mkuffd_wp(pmdswp);
I think it's fine to use *pmd, but maybe still better to use pmdval? I
worry pmdp_invalidate()) can be something else in the future that may
affect the bit.
Wondering how I ended up with that, I realized that it's actually
wrong and might have worked by chance for my reproducer on x86.
That should make it work:
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f977c965fdad..fffc953fa6ea 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3257,7 +3257,7 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
pmdswp = swp_entry_to_pmd(entry);
if (pmd_soft_dirty(pmdval))
pmdswp = pmd_swp_mksoft_dirty(pmdswp);
- if (pmd_swp_uffd_wp(*pvmw->pmd))
+ if (pmd_uffd_wp(pmdval))
pmdswp = pmd_swp_mkuffd_wp(pmdswp);
set_pmd_at(mm, address, pvmw->pmd, pmdswp);
page_remove_rmap(page, vma, true);
I guess pmd_swp_uffd_wp() just reads the _USER bit 2 which is also set for
a present pte, but then it sets swp uffd-wp always even if it was not set.
Yes. I modified the reproducer to migrate without uffd-wp first and we
suddenly gain a uffd-wp bit.
Yes the change must be squashed in to be correct, with that, my R-b keeps.
Thanks, I will resend later.
--
Thanks,
David / dhildenb
