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[70.52.228.144]) by smtp.gmail.com with ESMTPSA id s11-20020a92cc0b000000b0030380d1e24bsm444093ilp.30.2023.01.06.07.13.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Jan 2023 07:13:23 -0800 (PST) Date: Fri, 6 Jan 2023 10:13:14 -0500 From: Peter Xu To: James Houghton Cc: Mike Kravetz , Muchun Song , David Hildenbrand , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 34/46] hugetlb: userfaultfd: when using MADV_SPLIT, round addresses to PAGE_SIZE Message-ID: References: <20230105101844.1893104-1-jthoughton@google.com> <20230105101844.1893104-35-jthoughton@google.com> MIME-Version: 1.0 In-Reply-To: <20230105101844.1893104-35-jthoughton@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DF213100007 X-Stat-Signature: 3kdadap33b17ubi497jx17j86zswdx55 X-HE-Tag: 1673018006-695862 X-HE-Meta: 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 z1JMdEYp QVhmHjQAZyHzur/r7KPbSwjHJFqG4eNmClUIxBfaWS4uZwMh/0IzbQahZldN72oytcSQ5V6pQf3TXyyaEcWAE7cfWhL+KulT9xOeDCYd4dZ9woDYMxDHq/mXPLQ2UjN+/2cTbMLzWeNOK/Atmxd/klGygBQ== 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 Thu, Jan 05, 2023 at 10:18:32AM +0000, James Houghton wrote: > MADV_SPLIT enables HugeTLB HGM which allows for UFFDIO_CONTINUE in > PAGE_SIZE chunks. If a huge-page-aligned address were to be provided, > userspace would be completely unable to take advantage of HGM. That > would then require userspace to know to provide > UFFD_FEATURE_EXACT_ADDRESS. > > This patch would make it harder to make a mistake. Instead of requiring > userspace to provide UFFD_FEATURE_EXACT_ADDRESS, always provide a usable > address. > > Signed-off-by: James Houghton > --- > mm/hugetlb.c | 31 +++++++++++++++---------------- > 1 file changed, 15 insertions(+), 16 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 5af6db52f34e..5b6215e03fe1 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5936,28 +5936,27 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma, > unsigned long addr, > unsigned long reason) > { > + u32 hash; > + struct vm_fault vmf; > + > /* > * Don't use the hpage-aligned address if the user has explicitly > * enabled HGM. > */ > if (hugetlb_hgm_advised(vma) && reason == VM_UFFD_MINOR) > - haddr = address & PAGE_MASK; > - > - u32 hash; > - struct vm_fault vmf = { > - .vma = vma, > - .address = haddr, > - .real_address = addr, > - .flags = flags, > + haddr = addr & PAGE_MASK; > > - /* > - * Hard to debug if it ends up being > - * used by a callee that assumes > - * something about the other > - * uninitialized fields... same as in > - * memory.c > - */ > - }; > + vmf.vma = vma; > + vmf.address = haddr; > + vmf.real_address = addr; > + vmf.flags = flags; Const fields here: mm/hugetlb.c: In function ‘hugetlb_handle_userfault’: mm/hugetlb.c:5961:17: error: assignment of member ‘vma’ in read-only object 5961 | vmf.vma = vma; | ^ mm/hugetlb.c:5962:21: error: assignment of member ‘address’ in read-only object 5962 | vmf.address = haddr; | ^ mm/hugetlb.c:5963:26: error: assignment of member ‘real_address’ in read-only object 5963 | vmf.real_address = addr; > + /* > + * Hard to debug if it ends up being > + * used by a callee that assumes > + * something about the other > + * uninitialized fields... same as in > + * memory.c > + */ PS: I think we can drop this along the way. > > /* > * vma_lock and hugetlb_fault_mutex must be dropped before handling > -- > 2.39.0.314.g84b9a713c41-goog > -- Peter Xu