[dpdk-dev] bug: virtio PMD sends malformed packets for 32-bit processes on 64-bit kernel

[Frederico Cadete]

Hello,

I believe commit 260aae9a [1] has introduced a regression for the case
of 32-bit process running on a 64-bit kernel.

The commit is effectively casting mbuf->buf_physaddr to uintptr_t
before dereferencing it. It truncates the physical address to the width
of the process's uint, and in the the aforementioned combination this
loses important bits.

I can confirm this under GDB. When virtqueue_enqueue_xmit is filling in
start_dp, I get this result:

(gdb) p /x cookie->buf_physaddr
$5 = 0x12f94a000
(gdb) p /x start_dp[idx].addr
$6 = 0x2f94a080

On my system, I capture the packet that goes out to the host and I see
it has the correct size but the content is all-zeroes.

I would like to propose a patch that would work for all supported
combinations of user/kernel bitwidth  *and* virtio-pci/virtio-user. But
I don't really see how that could work, given virtio-user tries to
store a physical address in rte_mbuf's "void *buf_addr", and this is
not always big enough for a physical address.
Any suggestions on if and how this could be fixed?

Meanwhile, the bug affects dpdk 17.05, 17.02.1 and master. Users not
requiring virtio-user support can avoid it by setting
CONFIG_VIRTIO_USER=n during compilation.

Best regards,
Frederico Cadete