Re: [Qemu-devel] [PATCH] e1000: Don't set the Capabilities List bit

[Philipp Hahn <hahn@univention.de>]

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Hello,

On Wednesday 21 September 2011 22:06:25 dann frazier wrote:
> The Capabilities Pointer is NULL, so this bit shouldn't be set. The state
> of this bit doesn't appear to change any behavior on Linux/Windows versions
> we've tested, but it does cause Windows' PCI/PCI Express Compliance Test to
> balk.
...
> +++ b/hw/e1000.c
> @@ -1151,8 +1151,6 @@ static int pci_e1000_init(PCIDevice *pci_dev)
...
> -    /* TODO: we have no capabilities, so why is this bit set? */
> -    pci_set_word(pci_conf + PCI_STATUS, PCI_STATUS_CAP_LIST);

I think that change introduced a upgrade problem:
We have several VMs initially setup with qemu-0.12 and 0.14. Over the time of 
years we've created lots of snapshots, which we'd like to keep.
Now it's time to upgrade qemu(-kvm) on our hosts to qemu-1.1.2, but trying to 
load the old save states failes with
  qemu: warning: error while loading state for instance 0x0 of 
device '0000:00:03.0/e1000'

I traced it down to get_pci_config_device() failung for the e1000, because of 
that changed bit:
(gdb) print /x config@256 
$23 = {0x86, 0x80, 0xe, 0x10, 0x7, 0x0, 0x18, 0x0, 0x3, 0x0, 0x0, 0x2, 0x0, 
0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0xf2, 0x41, 0xc0, 0x0 <repeats 22 times>, 0xf4, 
0x1a, 0x0, 0x11, 0x0,  0x0, 0x4, 0xf2, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 
0x0, 0xb, 0x1, 0x0 <repeats 194 times>}
(gdb) print /x *s->config@256 
$25 = {0x86, 0x80, 0xe, 0x10, 0x0, 0x0, 0x0, 0x0, 0x3, 0x0, 0x0, 0x2, 0x0, 
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x1, 0x0 <repeats 23 times>, 0xf4, 0x1a, 
0x0, 0x11, 0x0 <repeats 13 times>, 0x1, 0x0 <repeats 194 times>}

Since cmask[PCI_STATUS=6] = PCI_STATUS_CAP_LIST=0x10 marks that bit as 
unmodifiable, the functions returns an error and aborts loading the saved 
state.

Is this problem known?
Is such an upgrade of qemu supposed to work?
Has somebody an idea how to fix this issue?

Sincerely
Philipp Hahn

PS: It would be nice if the error message could indicate an error because of 
an incompatible PCI configuration. I had a very similar problem with the 
rtl8139 card, where the ROM size was changed due to the upgrade from 
etherboot to iPXE.
PPS: It's slightly confusing to get a 'warning' message starting with 'error 
loading ...'
-- 
Philipp Hahn           Open Source Software Engineer      hahn@univention.de
Univention GmbH        be open.                       fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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