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[2003:cb:c703:fe00:10fe:298:6bf1:d163]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-52ca282f1e6sm121385e87.88.2024.06.13.01.07.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Jun 2024 01:07:18 -0700 (PDT) Message-ID: <818f69fa-9dc7-4ca0-b3ab-a667cd1fb16d@redhat.com> Date: Thu, 13 Jun 2024 10:07:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 06/11] filemap: cap PTE range to be created to allowed zero fill in folio_map_range() To: Luis Chamberlain , Matthew Wilcox , Hugh Dickins , yang@os.amperecomputing.com, linmiaohe@huawei.com, muchun.song@linux.dev, osalvador@suse.de Cc: "Pankaj Raghav (Samsung)" , david@fromorbit.com, djwong@kernel.org, chandan.babu@oracle.com, brauner@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, hare@suse.de, linux-kernel@vger.kernel.org, Zi Yan , linux-xfs@vger.kernel.org, p.raghav@samsung.com, linux-fsdevel@vger.kernel.org, hch@lst.de, gost.dev@samsung.com, cl@os.amperecomputing.com, john.g.garry@oracle.com References: <20240607145902.1137853-1-kernel@pankajraghav.com> <20240607145902.1137853-7-kernel@pankajraghav.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 10DE0140007 X-Stat-Signature: pt99waan4sp67gusayr4urey41m5s6h5 X-HE-Tag: 1718266046-205787 X-HE-Meta: U2FsdGVkX1980u6XDLa2exW4gi//pPeV0K0sFW3yYs2tyCD33RhJiS47zdkLvmRZOOfzMwnUwuWPQU8XFMHKt+JuKgd7DAI07LZE7fOZQLaBu92R19dPIp3riTb3FU/5ibB9YENbaK206BnleLZB91rc2uckiNa67eWTnOvpVfyBo2+gbXqCKpgA3aMEHfnimVpUBwpm+NfsDEJDIUAUxUbi86O6HNUzNXXAZMWZyQtwndeKNc+UfONypMFn6mjZJKhISw2EGl66e0VRd1UUfX6V87fafuHIW+S3SRh2C2qKSL7Oyx7Qn4ZNJrcYwJGnr4ZJbfeju4OEHXVd70cc9oESXUF4cXxaiSdmhOUyMATtNR2+XsPLDD2X6kuLjPaTwkQFkHrCnNka0RGXQz8mPawzJgwuSe0U1ZLLlOoOvHeh6yszjj8Nr3BMFde8U/m6IwP2nJYS1/LsPdsG3GJwBnllKDvajVMJdA7sX5W8bn3eWmiHjBTpch/OuW41wSI+h/JtHo/UsI87FefMr3Knu1HOL6QGzcG8heAcN+1BGnd98jjvVp5TKpOWR6qy+jw13OV8jpD7sejlRdrGEwDYTZ/MFizxaW/aLNx92/DjH/c37LtzTf/+lxmLF7fNVF0EIhNE9DV6QfTthSQkRU6sYl0cIGg2u2ub1pSX4D0NkkZWPHR7yd+KKVdt6FCT50R8qAzfAhYvGYXnI5mWq2LQHsJCHRV85U62bx1F1Y1kZMu6fpg+kC7mnm1ySEYYBfznByt9h1wY1kMuYoPSTa2zZ1GwDGt3KW2Y5yNIr1i8il+cFU5hwL7dqoD0GQT6yAmjFTVUgTTKryEfew6xrcNEklobmEqh3Bmv5hwq8VyL1u5r8vhWD/k6mONnP94mRcWHYSEYe+K7+/MtLNaJX0S2+Zc4ha5dEIgMrKY3zFFXg4kpJRVl+TrAZ1MsAYejWSNwjJFTJV9CQu19Nz4wCrF fCrNnB1f 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 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: List-Subscribe: List-Unsubscribe: On 13.06.24 09:57, Luis Chamberlain wrote: > On Wed, Jun 12, 2024 at 08:08:15PM +0100, Matthew Wilcox wrote: >> On Fri, Jun 07, 2024 at 02:58:57PM +0000, Pankaj Raghav (Samsung) wrote: >>> From: Pankaj Raghav >>> >>> Usually the page cache does not extend beyond the size of the inode, >>> therefore, no PTEs are created for folios that extend beyond the size. >>> >>> But with LBS support, we might extend page cache beyond the size of the >>> inode as we need to guarantee folios of minimum order. Cap the PTE range >>> to be created for the page cache up to the max allowed zero-fill file >>> end, which is aligned to the PAGE_SIZE. >> >> I think this is slightly misleading because we might well zero-fill >> to the end of the folio. The issue is that we're supposed to SIGBUS >> if userspace accesses pages which lie entirely beyond the end of this >> file. Can you rephrase this? >> >> (from mmap(2)) >> SIGBUS Attempted access to a page of the buffer that lies beyond the end >> of the mapped file. For an explanation of the treatment of the >> bytes in the page that corresponds to the end of a mapped file >> that is not a multiple of the page size, see NOTES. >> >> >> The code is good though. >> >> Reviewed-by: Matthew Wilcox (Oracle) > > Since I've been curating the respective fstests test to test for this > POSIX corner case [0] I wanted to enable the test for tmpfs instead of > skipping it as I originally had it, and that meant also realizing mmap(2) > specifically says this now: > > Huge page (Huge TLB) mappings Confusion alert: this likely talks about hugetlb (MAP_HUGETLB), not THP and friends. So it might not be required for below changes. > ... > For mmap(), offset must be a multiple of the underlying huge page > size. The system automatically aligns length to be a multiple of > the underlying huge page size. > > So do we need to adjust this patch with this: > > diff --git a/mm/filemap.c b/mm/filemap.c > index ea78963f0956..9c8897ba90ff 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3617,6 +3617,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > vm_fault_t ret = 0; > unsigned long rss = 0; > unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved, folio_type; > + unsigned int align = PAGE_SIZE; > > rcu_read_lock(); > folio = next_uptodate_folio(&xas, mapping, end_pgoff); > @@ -3636,7 +3637,10 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > goto out; > } > > - file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; > + if (folio_test_pmd_mappable(folio)) > + align = 1 << folio_order(folio); > + > + file_end = DIV_ROUND_UP(i_size_read(mapping->host), align) - 1; > if (end_pgoff > file_end) > end_pgoff = file_end; > > [0] https://lore.kernel.org/all/20240611030203.1719072-3-mcgrof@kernel.org/ > > Luis > -- Cheers, David / dhildenb