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 222l0PvG 6aBCR96gRGM13w4laOHpELuhgNtNPA3CNcUFzfPJPY4W7iWQWlBHLfbSHA1it2EqcipQjdmLOLlT5MOzgqaVJFuv3g7iJkRoSEEwyIdTN0ly3ej3u9ZrpE8Zqz63ie6/MLOb80CSmV1Aub1o79wANYfK2z4l5M2dX7Lhg/J2LE/83cdrzibGpcweB9K5CBFOmj/a+io0Vwy1gzyoc5+sRE8GsglERYjtCf9gByDXk3S9gnv77Ct8e/8bmRyKYesuojKUw1H191uE4HGRWAq6uLKy7t8wig5msxbkDq5Gb6LB5aKmLg80foCeeqYij8oaq2qBF/NFzBWWFeJWN+bwnT4ECK8/h23sLI5xSjReGG2oXnRJ8bLMyinzjNjAkakwewbZm X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 01/24/23 18:00, Peter Xu wrote: > On Tue, Jan 24, 2023 at 12:56:24PM -0800, Mike Kravetz wrote: > > At first thought this seems bad. However, I believe this has been the > > behavior since hugetlb PMD sharing was introduced in 2006 and I am > > unaware of any reported issues. I did a audit of code looking at > > mapcount. In addition to the above issue with smaps, there appears > > to be an issue with 'migrate_pages' where shared pages could be migrated > > without appropriate privilege. > > > > /* With MPOL_MF_MOVE, we migrate only unshared hugepage. */ > > if (flags & (MPOL_MF_MOVE_ALL) || > > (flags & MPOL_MF_MOVE && page_mapcount(page) == 1)) { > > if (isolate_hugetlb(page, qp->pagelist) && > > (flags & MPOL_MF_STRICT)) > > /* > > * Failed to isolate page but allow migrating pages > > * which have been queued. > > */ > > ret = 1; > > } > > > > I will prepare fixes for both of these. However, I wanted to ask if > > anyone has ideas about other potential issues with this? > > This reminded me whether things should be checked already before this > happens. E.g. when trying to share pmd, whether it makes sense to check > vma mempolicy before doing so? Not sure I understand your question. Are you questioning whether we should enter into pmd sharing if mempolicy allows movement to another node? Wouldn't this be the 'normal' case on a multi-node system? > Then the question is if pmd sharing only happens with the vma that shares > the same memory policy, whether above mapcount==1 check would be acceptable > even if it's shared by multiple processes. I am not a mempolicy expert, but that would still involve moving pages mapped by another process. For that CAP_SYS_NICE is required. So, my opinion would be that it is not allowed even if mempolicy is the same. > Besides, I'm also curious on the planned fix too regarding the two issues > mentioned. My planned 'fix' is to simply check for shared a PMD (page_count(virt_to_page(pte))) to determine if page with mapcount == 1 is shared. -- Mike Kravetz