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Date: Wed, 24 Aug 2011 14:29:36 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Qemu-devel] [PATCH] pci: Error on PCI capability collisions
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

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 <alex.williamson@redhat.com>
>>>>
>>>> Nothing good can happen when we overlap capabilities
>>>>
>>>> [ Jan: rebased over qemu, minor formatting ]
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> This doesn't build for me:
>>>
>>> /scm/qemu/hw/pci.c: In function =E2=80=98pci_add_capability=E2=80=99:
>>> /scm/qemu/hw/pci.c:1970:45: error: =E2=80=98PCIDevice=E2=80=99 has no=
 member named =E2=80=98config_map=E2=80=99
>>
>> Yeah, sorry, forgot to refresh the commit before posting.
>>
>>>
>>> I think that what that includes is the capability including each give=
n
>>> 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=
)
>>> {                                      =20
>>>     uint8_t next, prev, found =3D 0;
>>>
>>>     if (!(pdev->config[PCI_STATUS] & PCI_STATUS_CAP_LIST))
>>>         return 0;
>>>
>>>     for (prev =3D PCI_CAPABILITY_LIST; (next =3D pdev->config[prev]);
>>>          prev =3D next + PCI_CAP_LIST_NEXT)
>>>         if (next <=3D offset && next > found)
>>>             found =3D next;
>>>
>>>     return found;
>>> }
>>
>> Sounds useful, will enhance the patch.
>>
>> (Originally, I just wanted to reduce the qemu-kvm delta... :) )
>>
>> Jan
>=20
> 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

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