Re: [Xen-devel] [PATCH v2] pci: a workaround for nonstandard PCI devices whose PBA shares

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.18 at 16:10, <chao.gao@xxxxxxxxx> wrote:
> On Mon, Apr 09, 2018 at 07:40:15AM -0600, Jan Beulich wrote:
>>I'm not convinced though that a global option is well suited here:
>>Exposing the device in this way may be okay for one guest, but
>>not for another. With your model one would need to reboot the
>>entire host for such a usage change.
>>
>>Furthermore boot time specification of SBDF is a problem with the
>>Dom0 kernel possibly re-organizing the topology, and is not going
>>to work well with hot-plugged devices.
> 
> Point taken. But one concern is if we don't specify devices at boot time
> whether PVH dom0 can use such devices (in my understanding, PVH dom0
> will use EPT, it will meet the same issue as HVM domU). If not, we need
> treat dom0 as an exception; pages where PBA resides won't be marked as
> read-only. But mmio_ro_ranges is global. Maybe build two separate
> mmio_ro_ranges for dom0 and domU?

Boot time Dom0 settings can come from the command line. But
already for hot-plugged devices (which go to Dom0 as well) this
approach would break. Generally permitting Dom0 write access
here is certainly an option, but strictly only as long as the MSI-X
table won't also become writable.

Jan


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