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Date: Thu, 30 Jan 2014 20:02:23 -0500 From: Richard Yao <ryao@...too.org> To: David Miller <davem@...emloft.net> Cc: "ericvh@...il.com" <ericvh@...il.com>, "rminnich@...dia.gov" <rminnich@...dia.gov>, "lucho@...kov.net" <lucho@...kov.net>, "v9fs-developer@...ts.sourceforge.net" <v9fs-developer@...ts.sourceforge.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel@...too.org" <kernel@...too.org>, "aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>, "will.deacon@....com" <will.deacon@....com>, "cov@...eaurora.org" <cov@...eaurora.org>, "behlendorf1@...l.gov" <behlendorf1@...l.gov>, "mthode@...ode.org" <mthode@...ode.org> Subject: Re: [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers On Jan 30, 2014, at 7:44 PM, David Miller <davem@...emloft.net> wrote: > From: David Miller <davem@...emloft.net> > Date: Thu, 30 Jan 2014 16:29:26 -0800 (PST) > >> From: Richard Yao <ryao@...too.org> >> 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 <ryao@...too.org> >>> Acked-by: Alexander Graf <agraf@...e.de> >>> Reviewed-by: Will Deacon <will.deacon@....com> >> >> Applied, thanks. > > Actually I had to revert, is_vmalloc_or_malloc_addr() is not exported to > modules, so this change breaks the build. Thanks for catching that. I had originally used is_vmalloc_addr() instead of is_vmalloc_or_malloc_addr(), but changed it after realizing this did not correct the problem on all architectures. The is_vmalloc_addr() lives in headers. I will send out a patch to get that symbol exported and resubmit this after it is merged.-- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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