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[195.135.220.15]) by mx.google.com with ESMTPS id x54si20871631edd.148.2019.07.30.23.15.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Jul 2019 23:15:38 -0700 (PDT) Received-SPF: pass (google.com: domain of jgross@suse.com designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jgross@suse.com designates 195.135.220.15 as permitted sender) smtp.mailfrom=jgross@suse.com X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 05D0CAD1E; Wed, 31 Jul 2019 06:15:37 +0000 (UTC) Subject: Re: [PATCH] xen/gntdev.c: Replace vm_map_pages() with vm_map_pages_zero() To: Souptick Joarder , marmarek@invisiblethingslab.com, sstabellini@kernel.org, boris.ostrovsky@oracle.com Cc: linux@armlinux.org.uk, willy@infradead.org, linux-mm@kvack.org, akpm@linux-foundation.org, gregkh@linuxfoundation.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <1564511696-4044-1-git-send-email-jrdr.linux@gmail.com> From: Juergen Gross Message-ID: <436440f5-0031-5ad5-4a22-2acf218ad727@suse.com> Date: Wed, 31 Jul 2019 08:15:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1564511696-4044-1-git-send-email-jrdr.linux@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: de-DE Content-Transfer-Encoding: 8bit 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 30.07.19 20:34, Souptick Joarder wrote: > 'commit df9bde015a72 ("xen/gntdev.c: convert to use vm_map_pages()")' > breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_pages() > will: > - use map->pages starting at vma->vm_pgoff instead of 0 > - verify map->count against vma_pages()+vma->vm_pgoff instead of just > vma_pages(). > > In practice, this breaks using a single gntdev FD for mapping multiple > grants. > > relevant strace output: > [pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0 > [pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7, 0) = > 0x777f1211b000 > [pid 857] ioctl(7, IOCTL_GNTDEV_SET_UNMAP_NOTIFY, 0x7ffd3407b710) = 0 > [pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0 > [pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7, > 0x1000) = -1 ENXIO (No such device or address) > > details here: > https://github.com/QubesOS/qubes-issues/issues/5199 > > The reason is -> ( copying Marek's word from discussion) > > vma->vm_pgoff is used as index passed to gntdev_find_map_index. It's > basically using this parameter for "which grant reference to map". > map struct returned by gntdev_find_map_index() describes just the pages > to be mapped. Specifically map->pages[0] should be mapped at > vma->vm_start, not vma->vm_start+vma->vm_pgoff*PAGE_SIZE. > > When trying to map grant with index (aka vma->vm_pgoff) > 1, > __vm_map_pages() will refuse to map it because it will expect map->count > to be at least vma_pages(vma)+vma->vm_pgoff, while it is exactly > vma_pages(vma). > > Converting vm_map_pages() to use vm_map_pages_zero() will fix the > problem. > > Marek has tested and confirmed the same. > > Reported-by: Marek Marczykowski-Górecki > Signed-off-by: Souptick Joarder > Tested-by: Marek Marczykowski-Górecki Pushed to xen/tip.git for-linus-5.3a Juergen