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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

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.

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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