Re: [Xen-devel] [PATCH] libxl: suppress device assignment to HVM guest when there is no IOMMU

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

George Dunlap wrote on 2013-07-01:
> On Mon, Jul 1, 2013 at 2:45 PM, George Dunlap
> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>> On Mon, Jul 1, 2013 at 2:08 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>> This in effect copies similar logic from xend: While there's no way to
>>> check whether a device is assigned to a particular guest,
>>> XEN_DOMCTL_test_assign_device at least allows checking whether an
>>> IOMMU is there and whether a device has been assign to _some_ guest.
>>> For the time being, this should be enough to cover for the missing
>>> error checking/recovery in other parts of libxl's device assignment
>>> paths.
>>> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> Something isn't quite right about this patch:
>> 
>> # xl create h0
>> Parsing config from h0
>> xc: info: VIRTUAL MEMORY ARRANGEMENT:
>>   Loader:        0000000000100000->000000000019ee28 Modules:      
>>   0000000000000000->0000000000000000 TOTAL:        
>>   0000000000000000->00000001ff800000 ENTRY ADDRESS: 0000000000100608
>>   xc: info: PHYSICAL MEMORY ALLOCATION: 4KB PAGES: 0x0000000000000200
>>   2MB PAGES: 0x00000000000007fb 1GB PAGES: 0x0000000000000004
>> libxl: error: libxl_pci.c:1046:libxl__device_pci_add: PCI device
>> 0000:07:00.0 cannot be assigned - no IOMMU?
>> Daemon running with PID 3468
>> # xl pci-list h0
>> Vdev Device
>> 00.0 0000:07:00.0
>> # xl pci-assignable-list
>> #
>> 
>> In other words, the xenstore stuff is still happening.
Still got confused. If no IOMMU, why there will have device assignable? But I 
think there may no good way to solve it since pci-assignalbe-list don't need 
IOMMU's intercept. Perhaps we should show whether IOMMU is enabled with 'xl 
pci-assignable-list ' to let user know more earlier.

> 
> OK, I think this patch is probably still a good thing to take.  It
> does result in the device getting "stuck" in this intermetidate state
> until the domain shuts down (can't assign it to someone else, can't
> pci-detach either); but once the domain does shut down, everything
> goes back to normal.  That's better than the potential data corruption
> / security issue we had before.
> 
> Tested-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> 
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Best regards,
Yang


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