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[2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a]) by smtp.gmail.com with ESMTPSA id z14-20020a5d640e000000b002bfb5bda59asm4467446wru.25.2023.01.27.08.23.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Jan 2023 08:24:00 -0800 (PST) Message-ID: Date: Fri, 27 Jan 2023 17:23:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 2/2] migrate: hugetlb: Check for hugetlb shared PMD in node migration Content-Language: en-US To: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Naoya Horiguchi , James Houghton , Peter Xu , Michal Hocko , Yang Shi , Vishal Moola , Matthew Wilcox , Muchun Song , Andrew Morton , stable@vger.kernel.org References: <20230126222721.222195-1-mike.kravetz@oracle.com> <20230126222721.222195-3-mike.kravetz@oracle.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230126222721.222195-3-mike.kravetz@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26.01.23 23:27, Mike Kravetz wrote: > migrate_pages/mempolicy semantics state that CAP_SYS_NICE is required > to move pages shared with another process to a different node. > page_mapcount > 1 is being used to determine if a hugetlb page is shared. > However, a hugetlb page will have a mapcount of 1 if mapped by multiple > processes via a shared PMD. As a result, hugetlb pages shared by multiple > processes and mapped with a shared PMD can be moved by a process without > CAP_SYS_NICE. > > To fix, check for a shared PMD if mapcount is 1. If a shared PMD is > found consider the page shared. > > Fixes: e2d8cf405525 ("migrate: add hugepage migration code to migrate_pages()") > Cc: stable@vger.kernel.org > Signed-off-by: Mike Kravetz > --- > mm/mempolicy.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 85a34f1f3ab8..72142fbe7652 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -600,7 +600,8 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask, > > /* With MPOL_MF_MOVE, we migrate only unshared hugepage. */ > if (flags & (MPOL_MF_MOVE_ALL) || > - (flags & MPOL_MF_MOVE && page_mapcount(page) == 1)) { > + (flags & MPOL_MF_MOVE && page_mapcount(page) == 1 && > + !hugetlb_pmd_shared(pte))) { > if (isolate_hugetlb(page, qp->pagelist) && > (flags & MPOL_MF_STRICT)) > /* Acked-by: David Hildenbrand -- Thanks, David / dhildenb