Re: [Xen-devel] [PATCH QEMU-XEN] xen/pt: Start with emulated PCI_COMMAND set to zero.

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Thursday, June 11, 2015, 9:47:47 AM, you wrote:

>>>> On 10.06.15 at 22:53, <konrad@xxxxxxxxxx> wrote:
>> --- a/hw/xen/xen_pt.c
>> +++ b/hw/xen/xen_pt.c
>> @@ -785,7 +785,9 @@ out:
>>          xen_host_pci_set_word(&s->real_device, PCI_COMMAND,
>>                                pci_get_word(d->config + PCI_COMMAND) | cmd);
>>      }
>> -
>> +    /* Until the guest enables the device use d->config values which will
>> +     * inhibit pci_bar_address & pci_update_mappings from triggering 
>> updates.*/
>> +    pci_set_word(d->config + PCI_COMMAND, 0);
>>      memory_listener_register(&s->memory_listener, &address_space_memory);
>>      memory_listener_register(&s->io_listener, &address_space_io);
>>      XEN_PT_LOG(d,

> Well, I can see this as something to be tried out as an experiment,
> but it looks like you mean this to be a proper submission for
> inclusion upstream? Or maybe not, considering that qemu-devel
> wasn't even Cc-ed? In any case - what we need here is a general
> solution to at least the initialization part of the problem, i.e. all
> fields we emulate some or all bits for need to have d->config[]
> updated accordingly (i.e. you need to merge d->config[] and
> XenPTReg's data field based on the respective XenPTRegInfo's
> emu_mask, but perhaps simply copying the data field to
d->>config[] would have the same effect; if it doesn't, we have
> yet another problem). For the command register this for example
> means that it is in no way guaranteed that it would end up being
> zero; its emu_mask however guarantees that the memory and I/O
> decode bits would start out as zero (which is what you're after).

Just tested this patch together with a dom0 kernel which has the dropped kernel 
patch from Konrad:
22d8a8938407cb1342af763e937fdf9ee8daf24a xen/pciback: Don't disable PCI_COMMAND 
on PCI device reset.

And this patch does help to prevent the issue from happening.
 
--
Sander

> Jan




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