On 12.10.2021 11:38, Oleksandr Andrushchenko wrote: > On 12.10.21 12:32, Jan Beulich wrote: >> On 12.10.2021 10:41, Bertrand Marquis wrote: >>>> On 12 Oct 2021, at 09:29, Jan Beulich <jbeul...@suse.com> wrote: >>>> On 11.10.2021 19:11, Bertrand Marquis wrote: >>>>>> On 11 Oct 2021, at 17:32, Roger Pau Monné <roger....@citrix.com> wrote: >>>>>> On Mon, Oct 11, 2021 at 02:16:19PM +0000, Bertrand Marquis wrote: >>>>>>>> On 11 Oct 2021, at 14:57, Roger Pau Monné <roger....@citrix.com> wrote: >>>>>>>> I think the commit message needs to at least be expanded in order to >>>>>>>> contain the information provided here. It might also be helpful to >>>>>>>> figure out whether we would have to handle IO port accesses in the >>>>>>>> future on Arm, or if it's fine to just ignore them. >>>>>>> All our investigations and tests have been done without supporting it >>>>>>> without any issues so this is not a critical feature (most devices can >>>>>>> be operated without using the I/O ports). >>>>>> IMO we should let the users know they attempted to use a device with >>>>>> BARs in the IO space, and that those BARs won't be accessible which >>>>>> could make the device not function as expected. >>>>>> >>>>>> Do you think it would be reasonable to attempt the hypercall on Arm >>>>>> also, and in case of error (on Arm) just print a warning message and >>>>>> continue operations as normal? >>>>> I think this would lead to a warning printed on lots of devices where in >>>>> fact there would be no issues. >>>>> >>>>> If this is an issue for a device driver because it cannot operate without >>>>> I/O ports, this will be raised by the driver inside the guest. >>>> On what basis would the driver complain? The kernel might know of >>>> the MMIO equivalent for ports, and hence might allow the driver >>>> to properly obtain whatever is needed to later access the ports. >>>> Just that the port accesses then wouldn't work (possibly crashing >>>> the guest, or making it otherwise misbehave). >>> As ECAM and Arm does not support I/O ports, a driver requesting access >>> to them would get an error back. >>> So in practice it is not possible to try to access the ioports as there is >>> no >>> way on arm to use them (no instructions). >>> >>> A driver could misbehave by ignoring the fact that ioports are not there but >>> I am not quite sure how we could solve that as it would be a bug in the >>> driver. >> The minimal thing I'd suggest (or maybe you're doing this already) >> would be to expose such BARs to the guest as r/o zero, rather than >> letting their port nature "shine through". > If we have the same, but baremetal then which entity disallows > those BARs to shine?
I'm sorry, but I don't understand what you're trying to say. > I mean that if guest wants to crash... why > should we stop it and try emulating something special for it? This isn't about a guest "wanting to crash", but a driver potentially getting mislead into thinking that it can driver a device a certain way. Jan
