Re: [Xen-devel] [PATCH v2] VT-d: don't pass bridge devices to domain_context_mapping_one()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.01.2020 17:07, Roger Pau Monné  wrote:
> On Mon, Jan 20, 2020 at 04:42:22PM +0100, Jan Beulich wrote:
>> --- a/xen/drivers/passthrough/vtd/iommu.c
>> +++ b/xen/drivers/passthrough/vtd/iommu.c
>> @@ -1493,18 +1493,28 @@ static int domain_context_mapping(struct
>>          if ( find_upstream_bridge(seg, &bus, &devfn, &secbus) < 1 )
>>              break;
>>  
>> +        /*
>> +         * Mapping a bridge should, if anything, pass the struct pci_dev of
>> +         * that bridge. Since bridges don't normally get assigned to guests,
>> +         * their owner would be the wrong one. Pass NULL instead.
>> +         */
>>          ret = domain_context_mapping_one(domain, drhd->iommu, bus, devfn,
>> -                                         pci_get_pdev(seg, bus, devfn));
>> +                                         NULL);
>>  
>>          /*
>>           * Devices behind PCIe-to-PCI/PCIx bridge may generate different
>>           * requester-id. It may originate from devfn=0 on the secondary bus
>>           * behind the bridge. Map that id as well if we didn't already.
>> +         *
>> +         * Somewhat similar as for bridges, we don't want to pass a struct
>> +         * pci_dev here - there may not even exist one for this (secbus,0,0)
>> +         * tuple. If there is one, without properly working device groups it
>> +         * may again not have the correct owner.
>>           */
>>          if ( !ret && pdev_type(seg, bus, devfn) == DEV_TYPE_PCIe2PCI_BRIDGE 
>> &&
>>               (secbus != pdev->bus || pdev->devfn != 0) )
>>              ret = domain_context_mapping_one(domain, drhd->iommu, secbus, 0,
>> -                                             pci_get_pdev(seg, secbus, 0));
>> +                                             NULL);
> 
> Isn't it dangerous to map this device to the guest, and that multiple
> guests might end up with the same device mapped?

They won't (afaict) - see the checking done by domain_context_mapping_one()
when it finds an already present context entry. The first one to make such
a mapping will win.

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel