Re: [Qemu-devel] [PATCH] pci: Error on PCI capability collisions

[Jan Kiszka]

On 2011-08-24 14:34, Michael S. Tsirkin wrote:
> On Wed, Aug 24, 2011 at 02:29:36PM +0200, Jan Kiszka wrote:
>> On 2011-08-24 13:58, Michael S. Tsirkin wrote:
>>> On Wed, Aug 24, 2011 at 12:10:32PM +0200, Jan Kiszka wrote:
>>>> On 2011-08-24 12:04, Michael S. Tsirkin wrote:
>>>>> On Tue, Aug 23, 2011 at 07:28:08PM +0200, Jan Kiszka wrote:
>>>>>> From: Alex Williamson <address@hidden>
>>>>>>
>>>>>> Nothing good can happen when we overlap capabilities
>>>>>>
>>>>>> [ Jan: rebased over qemu, minor formatting ]
>>>>>>
>>>>>> Signed-off-by: Jan Kiszka <address@hidden>
>>>>>
>>>>> This doesn't build for me:
>>>>>
>>>>> /scm/qemu/hw/pci.c: In function ‘pci_add_capability’:
>>>>> /scm/qemu/hw/pci.c:1970:45: error: ‘PCIDevice’ has no member named 
>>>>> ‘config_map’
>>>>
>>>> Yeah, sorry, forgot to refresh the commit before posting.
>>>>
>>>>>
>>>>> I think that what that includes is the capability including each given
>>>>> offset, right?  It would be easy to write some code scanning the
>>>>> capability list to figure this value out.
>>>>> Something along the lines of (untested):
>>>>>
>>>>> static
>>>>> uint8_t pci_find_capability_at_offset(PCIDevice *pdev, uint8_t offset)
>>>>> {                                       
>>>>>     uint8_t next, prev, found = 0;
>>>>>
>>>>>     if (!(pdev->config[PCI_STATUS] & PCI_STATUS_CAP_LIST))
>>>>>         return 0;
>>>>>
>>>>>     for (prev = PCI_CAPABILITY_LIST; (next = pdev->config[prev]);
>>>>>          prev = next + PCI_CAP_LIST_NEXT)
>>>>>         if (next <= offset && next > found)
>>>>>             found = next;
>>>>>
>>>>>     return found;
>>>>> }
>>>>
>>>> Sounds useful, will enhance the patch.
>>>>
>>>> (Originally, I just wanted to reduce the qemu-kvm delta... :) )
>>>>
>>>> Jan
>>>
>>> Also, let's add a comment documenting the
>>> reason for this check: device assignment
>>> depends on this check to verify that the device
>>> is not broken.
>>
>> Based on the previous discussion, I don't think this is accurate as it
>> will also validate emulated devices.
>>
>> Jan
> 
> Something like the below is accurate, right?
> 
> /* Device assignment depends on this check to verify that the device
>    is not broken. Should never trigger for emulated devices,
>    but it's helpful for debugging these.
>  */

I've expressed this in the commit message. Unless there is another
reason to do v3, maybe you can merge the comment on commit.

Jan

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