Lorenzo Stoakes 35e2470326 mm: do not copy page tables unnecessarily for VM_UFFD_WP ... Commit ab04b530e7 ("mm: introduce copy-on-fork VMAs and make VM_MAYBE_GUARD one") aggregates flags checks in vma_needs_copy(), including VM_UFFD_WP. However in doing so, it incorrectly performed this check against src_vma. This check was done on the assumption that all relevant flags are copied upon fork. However the userfaultfd logic is very innovative in that it implements custom logic on fork in dup_userfaultfd(), including a rather well hidden case where lacking UFFD_FEATURE_EVENT_FORK causes VM_UFFD_WP to not be propagated to the destination VMA. And indeed, vma_needs_copy(), prior to this patch, did check this property on dst_vma, not src_vma. Since all the other relevant flags are copied on fork, we can simply fix this by checking against dst_vma. While we're here, we fix a comment against VM_COPY_ON_FORK (noting that it did indeed already reference dst_vma) to make it abundantly clear that we must check against the destination VMA. Link: https://lkml.kernel.org/r/20260114110006.1047071-1-lorenzo.stoakes@oracle.com Fixes: ab04b530e7 ("mm: introduce copy-on-fork VMAs and make VM_MAYBE_GUARD one") Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reported-by: Chris Mason <clm@meta.com> Closes: https://lore.kernel.org/all/20260113231257.3002271-1-clm@meta.com/ Acked-by: David Hildenbrand (Red Hat) <david@kernel.org> Acked-by: Pedro Falcato <pfalcato@suse.de> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>		2026-01-20 09:34:26 -08:00
..
acpi	ACPI: PCI: IRQ: Fix INTx GSIs signedness	2026-01-05 19:06:40 +01:00
asm-generic	mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather	2026-01-20 09:34:26 -08:00
clocksource	…
crypto	…
cxl	…
drm	drm-misc-fixes for v6.19-rc6:	2026-01-16 20:27:21 +01:00
dt-bindings	This pull request is entirely SoC clk drivers, not for lack of trying to modify	2025-12-08 09:38:52 +09:00
hyperv	hyperv: Avoid -Wflex-array-member-not-at-end warning	2025-12-18 19:42:01 +00:00
keys	…
kunit	kunit: Enforce task execution in {soft,hard}irq contexts	2025-12-22 12:20:08 -08:00
kvm	…
linux	mm: do not copy page tables unnecessarily for VM_UFFD_WP	2026-01-20 09:34:26 -08:00
math-emu	…
media	…
memory	…
misc	…
net	net: add net.core.qdisc_max_burst	2026-01-13 10:12:11 +01:00
pcmcia	…
ras	Significant patch series in this merge are as follows:	2025-12-05 13:52:43 -08:00
rdma	…
rv	…
scsi	scsi: core: Fix error handler encryption support	2026-01-04 15:16:20 -05:00
soc	This pull request is entirely SoC clk drivers, not for lack of trying to modify	2025-12-08 09:38:52 +09:00
sound	ALSA: pcm: Improve the fix for race of buffer access at PCM OSS layer	2026-01-08 08:07:54 +01:00
target	…
trace	nfsd-6.19 fixes:	2026-01-06 09:12:52 -08:00
uapi	Landlock fix for v6.19-rc6	2026-01-18 15:15:47 -08:00
ufs	…
vdso	…
video	…
xen	…
Kbuild	…