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@linux.alibaba.com
[ 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/635f43bdd85ac2615a58405da82b4d33c6e5eb05.166201756... Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages") Signed-off-by: Baolin Wang baolin.wang@linux.alibaba.com Suggested-by: Mike Kravetz mike.kravetz@oracle.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Cc: David Hildenbrand david@redhat.com Cc: Muchun Song songmuchun@bytedance.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org [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-FoCTp0KtF8ngGix289G2Q...
Please fix up and resend.
thanks,
greg k-h