Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs
From: Boris Ostrovsky
Date: Wed Apr 13 2016 - 15:12:12 EST
On 04/13/2016 01:36 PM, Boris Ostrovsky wrote:
On 04/12/2016 09:27 PM, Boris Ostrovsky wrote:
On 04/12/2016 07:15 PM, Stefano Stabellini wrote:
On Tue, 12 Apr 2016, Boris Ostrovsky wrote:
On 04/12/2016 05:56 PM, Stefano Stabellini wrote:
I am not sure, maybe you didn't have CONFIG_SPARSE_IRQ?
But I am certain that 4.6-rc2, with the attached config, fails as
Dom0
on QEMU with the following sequence of calls:
I did have CONFIG_SPARSE_IRQ and I just rebuilt 4.5.0 with your config
(4.6-rc3 doesn't build for me for some reason) and that booted dom0
as well.
BTW, what do you mean by "dom0 on QEMU"?
I am running Xen and Linux inside a QEMU x86_64 emulated machine
(nested
virt).
This I, of course, never tried.
But given that things work in a single-level virt, doesn't this imply
that perhaps there is something in the emulation that's not quite right?
OK, so this *is* broken on single level virt as well. It's just that
we always end up using AHCI so lack of irq 14 (and 15) does not affect
the system. And I guess in QEMU case it's IDE only, right?
You patch does fix this but I wonder if we could change something in
probe_8259A() so that we can continue using nr_legacy_irqs(). Using
nr_legacy_irqs() and NR_IRQS_LEGACY at the same time is inconsistent
and may cause us headaches in the future.
I think we could use paravirt_has() feature that was added for similar
reason when we had a problem with RTC (commit
d8c98a1d1488747625ad6044d423406e17e99b7a). So we add paravirt_has(PIC)
which will only be set by dom0 and then probe_8259A() will not set
legacy_pic to null_legacy_pic when this flag is set.
Note that paravirt_has() is being removed by
http://lists.xenproject.org/archives/html/xen-devel/2016-04/msg01415.html so
presumably we'd use new struct x86_legacy_features instead (copying Luis
so that if this is acceptable he could add it to his next spin).
-boris
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