On Thu, Dec 18, 2014 at 05:22:19PM +0800, Amos Kong wrote:
> After enabled network debug of e1000 in Win2012-64r2 guest,
> Bus mastering of e1000 can't be enabled by e1000 driver. It
> caused guest can't get IP address.
>
> # bcdedit /debug on
> # bcdedit /dbgsettings net hostip:192.168.122.100 port:50000
> (We can use non-existed IP here, it's just used to pass the
> setup, not really use it)
>
> If we disable debug function, e1000 driver can enable bus
> mastering bit successfully, guest network is fine.
>
> This patch changed e1000 backend to enalbe bus mastering
> unconditionally as a workaround.
>
> Signed-off-by: Amos Kong <ak...@redhat.com>
> ---
> hw/net/e1000.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index ec9224b..82829ae 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -1544,8 +1544,15 @@ static void e1000_write_config(PCIDevice *pci_dev,
> uint32_t address,
>
> pci_default_write_config(pci_dev, address, val, len);
>
> - if (range_covers_byte(address, len, PCI_COMMAND) &&
> - (pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
> + if (range_covers_byte(address, len, PCI_COMMAND)) {
> + /*
> + * Some guest (eg: Win2012-64r2) doesn't enable bus mastering
> + * correctly, it caused guest network down. So we unconditionally
> + * enable PCI bus mastering and BM memory region for e1000 as
> + * a workaround.
> + */
> + pci_dev->config[PCI_COMMAND] |= PCI_COMMAND_MASTER;
> + memory_region_set_enabled(&pci_dev->bus_master_enable_region, true);
> qemu_flush_queued_packets(qemu_get_queue(s->nic));
> start_xmit(s);
> }This is weird. Are you sure there's not some guest behavior missing like the NIC option ROM leaving bus mastering enabled after the BIOS/EFI has booted, causing Windows debug to work on physical machines? Before we merge a hack like this we should understand the problem 100%. Stefan
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