Re: [Xen-devel] [PATCH] xen/pv: Add PV specific legacy_pic struct to expose legacy IRQs.

From: Jennifer Herbert
Date: Mon Mar 25 2019 - 10:23:43 EST




On 21/03/19 17:49, Jennifer Herbert wrote:


On 19/03/19 23:06, Boris Ostrovsky wrote:
On 3/19/19 4:02 PM, Jennifer Herbert wrote:
The ACPI tables doesn't always contain all IRQs for legacy devices
such as RTC. Since no PIC controller is visible for a PV linux guest,
under Xen, legacy_pic currently defaults to the null_legacy_pic - with
reports no legacy IRQs. Since the commit "rtc: cmos: Do not assume
irq 8 for rtc when there are no legacy irqs" by Hans de Goede
(commit id: a1e23a42f1bdc00e32fc4869caef12e4e6272f26), the rtc now
incorrectly decides it has no irq it can use, for some hardware.

This patch rectifies the problem by providing a xen legacy_pic
struct, which is much like the null_legacy_pic except that it
reports NR_IRQS_LEGACY irqs.
I assume this is for dom0?

Could there be the same problem with PVH dom0? (and if yes then this
should probably go into arch/x86/xen/enlighten.c).

-boris


I am doing this to fix a problem with dom0. DomU doesn't seem to have an RTC, and so it is unaffected.

I'm not familiar with PVH, but have now done some experiments. The RTC on PVH seems broken - but not quite in the same way as PV. More research is needed, however simply doing the same trick I did with PV will not fix the issue.

I'll look further into it.


The same problem does exist with PVH - however its worse with the presence of the IO-APIC, as with my patch it tries to set up with IRQ, and fails. I'm not sure how would be best to deal with this.
However, the RTC seems broken even for machines without the ACPI omission.
I can see fixing it for just PV doesn't seem too nice, but unsure how to fix this for PVH. I'm open to suggestions, but otherwise I'll put this on hold.