From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Date: Thu, 30 Jan 2014 16:44:51 -0800 (PST) Message-ID: <20140130.164451.873520736572570393.davem@davemloft.net> References: <1391104968-10258-1-git-send-email-ryao@gentoo.org> <1391104968-10258-2-git-send-email-ryao@gentoo.org> <20140130.162926.561686911250624301.davem@davemloft.net> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: ericvh@gmail.com, rminnich@sandia.gov, lucho@ionkov.net, v9fs-developer@lists.sourceforge.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel@gentoo.org, aneesh.kumar@linux.vnet.ibm.com, will.deacon@arm.com, cov@codeaurora.org, behlendorf1@llnl.gov, mthode@mthode.org To: ryao@gentoo.org Return-path: In-Reply-To: <20140130.162926.561686911250624301.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: David Miller Date: Thu, 30 Jan 2014 16:29:26 -0800 (PST) > From: Richard Yao > Date: Thu, 30 Jan 2014 13:02:48 -0500 > >> The 9p-virtio transport does zero copy on things larger than 1024 bytes >> in size. It accomplishes this by returning the physical addresses of >> pages to the virtio-pci device. At present, the translation is usually a >> bit shift. >> >> However, that approach produces an invalid page address when we >> read/write to vmalloc buffers, such as those used for Linux kernle >> modules. This causes QEMU to die printing: >> >> qemu-system-x86_64: virtio: trying to map MMIO memory >> >> This patch enables 9p-virtio to correctly handle this case. This not >> only enables us to load Linux kernel modules off virtfs, but also >> enables ZFS file-based vdevs on virtfs to be used without killing QEMU. >> >> Also, special thanks to both Avi Kivity and Alexander Graf for their >> interpretation of QEMU backtraces. Without their guidence, tracking down >> this bug would have taken much longer. >> >> Signed-off-by: Richard Yao >> Acked-by: Alexander Graf >> Reviewed-by: Will Deacon > > Applied, thanks. Actually I had to revert, is_vmalloc_or_malloc_addr() is not exported to modules, so this change breaks the build.