[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 02/11] xen/arm: vpl011: Add new hvm params in Xen for ring buffer/event setup
Hi Jan, On 06/03/17 12:41, Jan Beulich wrote: On 06.03.17 at 12:42, <julien.grall@xxxxxxx> wrote:I thought a bit more about those params. I think the name should be generic and not tie to pl011 because we may want to emulate different UART for the guest in the future.That's reasonable, but I continue to have reservations against the underlying approach here, namely ...Also, by re-using deprecated encoding it means that it will not be possible to use those parameters on x86 if you ever decide to emulate UART in Xen. I am not sure whether if you are happy with that?... with this in mind: If we wanted to do this for HVM guests, we'd indeed want the parameters. If we wanted this for PV guests, the model wouldn't fit at all. Plus what I'm not understanding (perhaps because most of the discussion around this seemed to be ARM-specific, and hence I've skipped reading through it) is - why is this UART emulation needed in the first place? We've never had a need for such on x86, afaia. Linaro has published a set of guidelines to guarantee a same guest image can run on multiple hypervisors (see [1]). This specification mandates the presence of a SBSA-compliant UART. I just realized the cover letter does not explain why we need to emulate a PL011 on ARM. Bhupinder can you detail it on the next version? Furthermore - how does this scale? I.e. what if other devices pop up wanting to be emulated? Or multiple UARTs? I think you can appreciate that using QEMU for emulating an UART is quite overkill. Also, we are expecting more people to look at providing mediation (such as Firmware access) within Xen as they are concerned about performance and certification. An idea to ensure the integrity of Xen would be to run this code at a lower level. Cheers,[1] https://www.linaro.org/app/resources/WhitePaper/VMSystemSpecificationForARM-v2.0.pdf -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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