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Message-ID: <Y6TQaZaB+PKObfNs@x1n> Date: Thu, 22 Dec 2022 16:47:21 -0500 From: Peter Xu <peterx@...hat.com> To: James Houghton <jthoughton@...gle.com> Cc: Mike Kravetz <mike.kravetz@...cle.com>, Muchun Song <songmuchun@...edance.com>, David Hildenbrand <david@...hat.com>, David Rientjes <rientjes@...gle.com>, Axel Rasmussen <axelrasmussen@...gle.com>, Mina Almasry <almasrymina@...gle.com>, Zach O'Keefe <zokeefe@...gle.com>, Manish Mishra <manish.mishra@...anix.com>, Naoya Horiguchi <naoya.horiguchi@....com>, "Dr . David Alan Gilbert" <dgilbert@...hat.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>, Baolin Wang <baolin.wang@...ux.alibaba.com>, Miaohe Lin <linmiaohe@...wei.com>, Yang Shi <shy828301@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH v2 35/47] userfaultfd: require UFFD_FEATURE_EXACT_ADDRESS when using HugeTLB HGM On Fri, Oct 21, 2022 at 04:36:51PM +0000, James Houghton wrote: > @@ -1990,6 +1990,17 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx, > ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM); > #ifndef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING > uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS_HGM; > +#else > + > + ret = -EINVAL; > + if ((uffdio_api.features & UFFD_FEATURE_MINOR_HUGETLBFS_HGM) && > + !(uffdio_api.features & UFFD_FEATURE_EXACT_ADDRESS)) This check needs to be done upon "features" or "ctx_features", rather than "uffdio_api.features". The latter is the one we'll report to the user only. > + /* > + * UFFD_FEATURE_MINOR_HUGETLBFS_HGM is mostly > + * useless without UFFD_FEATURE_EXACT_ADDRESS, > + * so require userspace to provide both. > + */ > + goto err_out; > #endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */ > #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ > > -- > 2.38.0.135.g90850a2211-goog > > -- Peter Xu
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