Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1378803

Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs

Show all headers | View raw

On 04/13/2016 06:38 PM, Stefano Stabellini wrote:
>
> 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.

Something like

legacy_pic_xen = null_legacy_pic;
legacy_pic_xen.nr_legacy_irqs = NR_IRQS_LEGACY;
legacy_pic = legacy_pic_xen;

?

>
>   
>> 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.

I think once the series above makes it to mainline x86_legacy_features 
would be the way to go --- that's what it is created for. Given that we 
are almost at rc4 I assume that would be 4.7.

Using paravirt_has() now will create merge headaches so it's probably 
not a good idea. We can either use your original patch or do what you 
suggested with legacy_pic_xen (both of which are backportable) and then 
switch to x86_legacy_features once it shows up in the tree.

-boris

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before  allocating descs for legacy IRQs Stefano Stabellini <sstabellini@kernel.org> - 2016-04-12 04:10 +0200
  Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-04-12 10:40 +0200
  Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-12 15:30 +0200
    Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Stefano Stabellini <sstabellini@kernel.org> - 2016-04-12 20:10 +0200
      Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-12 21:10 +0200
        Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Stefano Stabellini <sstabellini@kernel.org> - 2016-04-12 23:20 +0200
          Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-12 23:40 +0200
            Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-13 00:40 +0200
              Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Stefano Stabellini <sstabellini@kernel.org> - 2016-04-13 01:20 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-13 03:30 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-13 19:40 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-13 21:20 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-14 00:30 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Stefano Stabellini <sstabellini@kernel.org> - 2016-04-14 00:40 +0200
                Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-14 14:50 +0200
      Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs David Vrabel <david.vrabel@citrix.com> - 2016-04-14 15:50 +0200
        Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence  before allocating descs for legacy IRQs Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-14 16:50 +0200

csiph-web