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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qHBpV-00AWp6-DD; Wed, 05 Jul 2023 23:22:37 +0000 Date: Thu, 6 Jul 2023 00:22:37 +0100 From: Matthew Wilcox To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Rik van Riel , Michal Hocko , Peter Xu , Dave Hansen Subject: Re: mprotect and hugetlb mappings Message-ID: References: <20230705230808.GA41006@monkey> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230705230808.GA41006@monkey> X-Rspam-User: X-Stat-Signature: nuyj77opx7rbgyzaqbw94ficbdzabr8j X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 33E07A0011 X-HE-Tag: 1688599361-948191 X-HE-Meta: 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 Fx77tLwU 7JLt1KAWvzl8z5dQMYGH6Sgi0wjZ+ptBorDMxkCvml4sGtaA+9h/8oK6PEb7XPHbNrkKVulIh8yCRsOv/RKDO+FWCHbjaWkgz/G5otboyBe7LGEQXt1b0X2l9Ax/CRrlWmc72lt5Mukwnn4Y= 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 Wed, Jul 05, 2023 at 04:08:08PM -0700, Mike Kravetz wrote: > I was recently asked about the behavior of mprotect on a hugetlb > mapping where addr or addr+len is not hugetlb page size aligned. As > one might expect, EINVAL is returned in such cases. However, the man > page makes no mention of alignment requirements for hugetlb mappings. > > I am happy to submit man page updates if people agree this is the correct > behavior. We might even want to check alignment earlier in the code > path as we fail when trying to split the vma today. > > An alternative behavior would be to operate on whole hugetlb pages within > the range addr - addr+len. After a careful re-reading of the mprotect() man page, I suggest the following behaviour ... addr must be a multiple of the hpage size. Otherwise -EINVAL. len should be rounded up to hpage size. I wonder how likely this change would be to break userspace code. Maybe some test cases.