On Wed, 13 Apr 2016, Boris Ostrovsky wrote:
> 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. Maybe we could introduce a legacy_pic_xen in arch/x86/kernel/i8259.c or arch/x86/xen/enlighten.c? We could set legacy_pic = legacy_pic_xen from start_kernel, so that we can skip probe_8259A completely. > 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). I would prefer to come up with a fix that is backportable to 4.3, 4.4 and 4.5.
