On Wed, Dec 04, 2013 at 08:43:18PM +0000, Richard Yao wrote:
> 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@xxxxxxxxxx>
> ---
> net/9p/trans_virtio.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 9c5a1aa..5d1d04b 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -340,7 +340,10 @@ static int p9_get_mapped_pages(struct virtio_chan *chan,
> int count = nr_pages;
> while (nr_pages) {
> s = rest_of_page(data);
> - pages[index++] = kmap_to_page(data);
> + if (is_vmalloc_or_module_addr(data))
Can this really end up being a module address?
Will
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