On Mon, Dec 12, 2022 at 08:39:59AM +0100, Greg KH wrote:
> On Sun, Dec 11, 2022 at 06:51:48PM -0800, Samuel Mendoza-Jonas wrote:
> > From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> >
> > [ Upstream commit fac35ba763ed07ba93154c95ffc0c4a55023707f ]
> >
> > On some architectures (like ARM64), it can support CONT-PTE/PMD size
> > hugetlb, which means it can support not only PMD/PUD size hugetlb (2M and
> > 1G), but also CONT-PTE/PMD size(64K and 32M) if a 4K page size specified.
> >
> > So when looking up a CONT-PTE size hugetlb page by follow_page(), it will
> > use pte_offset_map_lock() to get the pte entry lock for the CONT-PTE size
> > hugetlb in follow_page_pte(). However this pte entry lock is incorrect
> > for the CONT-PTE size hugetlb, since we should use huge_pte_lock() to get
> > the correct lock, which is mm->page_table_lock.
> >
> > That means the pte entry of the CONT-PTE size hugetlb under current pte
> > lock is unstable in follow_page_pte(), we can continue to migrate or
> > poison the pte entry of the CONT-PTE size hugetlb, which can cause some
> > potential race issues, even though they are under the 'pte lock'.
> >
> > For example, suppose thread A is trying to look up a CONT-PTE size hugetlb
> > page by move_pages() syscall under the lock, however antoher thread B can
> > migrate the CONT-PTE hugetlb page at the same time, which will cause
> > thread A to get an incorrect page, if thread A also wants to do page
> > migration, then data inconsistency error occurs.
> >
> > Moreover we have the same issue for CONT-PMD size hugetlb in
> > follow_huge_pmd().
> >
> > To fix above issues, rename the follow_huge_pmd() as follow_huge_pmd_pte()
> > to handle PMD and PTE level size hugetlb, which uses huge_pte_lock() to
> > get the correct pte entry lock to make the pte entry stable.
> >
> > Mike said:
> >
> > Support for CONT_PMD/_PTE was added with bb9dd3df8ee9 ("arm64: hugetlb:
> > refactor find_num_contig()"). Patch series "Support for contiguous pte
> > hugepages", v4. However, I do not believe these code paths were
> > executed until migration support was added with 5480280d3f2d ("arm64/mm:
> > enable HugeTLB migration for contiguous bit HugeTLB pages") I would go
> > with 5480280d3f2d for the Fixes: targe.
> >
> > Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.1662017562.git.baolin.wang@xxxxxxxxxxxxxxxxx
> > Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > [5.4: Fixup contextual diffs before pin_user_pages()]
>
> Thanks, both now queued up.
I'm dropping this one now as it adds a build warning as reported here:
https://lore.kernel.org/r/CA+G9fYtdgLx0hrtGk7G8Jvt2GhY-FoCTp0KtF8ngGix289G2QQ@xxxxxxxxxxxxxx
Please fix up and resend.
thanks,
greg k-h
