Commit c3b31ea7 authored by Peter Xu's avatar Peter Xu Committed by Kefeng Wang
Browse files

mm/memory: fix missing pte marker for !page on pte zaps 

mainline inclusion
from mainline-v6.9-rc2
commit f8572367eaff6739e3bc238ba93b86cd7881c0ff
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9CHB4
CVE: NA

-------------------------------------------------

Commit 0cf18e839f64 of large folio zap work broke uffd-wp.  Now mm's uffd
unit test "wp-unpopulated" will trigger this WARN_ON_ONCE().

The WARN_ON_ONCE() asserts that an VMA cannot be registered with
userfaultfd-wp if it contains a !normal page, but it's actually possible.
One example is an anonymous vma, register with uffd-wp, read anything will
install a zero page.  Then when zap on it, this should trigger.

What's more, removing that WARN_ON_ONCE may not be enough either, because
we should also not rely on "whether it's a normal page" to decide whether
pte marker is needed.  For example, one can register wr-protect over some
DAX regions to track writes when UFFD_FEATURE_WP_ASYNC enabled, in which
case it can have page==NULL for a devmap but we may want to keep the
marker around.

Link: https://lkml.kernel.org/r/20240313213107.235067-1-peterx@redhat.com


Fixes: 0cf18e839f64 ("mm/memory: handle !page case in zap_present_pte() separately")
Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
(cherry picked from commit f8572367eaff6739e3bc238ba93b86cd7881c0ff)
Signed-off-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
parent d20511c9

mm/memory.c

+3 −1
Original line number Diff line number Diff line
@@ -1610,7 +1610,9 @@ static inline int zap_present_ptes(struct mmu_gather *tlb, 
		ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);

		arch_check_zapped_pte(vma, ptent);

		tlb_remove_tlb_entry(tlb, pte, addr);

		VM_WARN_ON_ONCE(userfaultfd_wp(vma));

		if (userfaultfd_pte_wp(vma, ptent))

			zap_install_uffd_wp_if_needed(vma, addr, pte, 1,

						      details, ptent);

		ksm_might_unmap_zero_page(mm, ptent);

		return 1;

	}