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Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10 |
Date: |
Wed, 27 Sep 2017 15:49:27 +0100 |
User-agent: |
Mutt/1.9.0 (2017-09-02) |
* Cornelia Huck (address@hidden) wrote:
> On Wed, 27 Sep 2017 15:28:38 +0100
> "Dr. David Alan Gilbert" <address@hidden> wrote:
>
> > * David Hildenbrand (address@hidden) wrote:
> > > On 27.09.2017 12:59, Christian Borntraeger wrote:
> > > >
> > > >
> > > > On 09/27/2017 12:56 PM, Cornelia Huck wrote:
> > > >> On Wed, 27 Sep 2017 18:25:00 +0800
> > > >> Yi Min Zhao <address@hidden> wrote:
> > > >>
> > > >>> 在 2017/9/27 下午5:47, Cornelia Huck 写道:
> > > >>>> On Tue, 26 Sep 2017 20:40:25 +0200
> > > >>>> David Hildenbrand <address@hidden> wrote:
> > > >>
> > > >>>>> I'd really really really (did I mention really?) favor something
> > > >>>>> like a
> > > >>>>> dummy device, because we could easily handle the !CONFIG_PCI case
> > > >>>>> then.
> > > >>>>>
> > > >>>>> All these compat options and conditions will kill us someday...
> > > >>>>> we're
> > > >>>>> already patching around that whole stuff way too much.
> > > >>>>>
> > > >>>>> If we ever unconditionally created a device, we should keep doing
> > > >>>>> so.
> > > >>>> Yes, that whole thing is horrible, especially interaction with compat
> > > >>>> machines.
> > > >>>>
> > > >>>> Do you have an idea on how to create such a dummy device (without
> > > >>>> having to effectively copy a lot of configured-out code)?
> > > >>>>
> > > >>>>
> > > >>> How about in s390_pcihost_hot_plug() we check s390_has_feat(zpci)?
> > > >>> If no zpci feature, we avoid plugging any pci device.
> > > >>> Then we could always create phb.
> > > >>> I think pcibus's vmstate is only data to migrate.
> > > >>
> > > >> That's still problematic if CONFIG_PCI is off. I currently don't have a
> > > >> better idea than either disallowing compat machines on builds without
> > > >> pci, or using a dummy device...
> > > >
> > > > For this particular case your initial patch might be less problematic
> > > > than
> > > > a dummy device, because the code that does the migration is NOT
> > > > contained
> > > > in s390 specific code but in common PCI code instead. We would need to
> > > > keep
> > > > the dummy device always in a way that it will work with the common PCI
> > > > code.
> > > >
> > >
> > > Interesting, so how is migration then handled for e.g. x86 or other
> > > architectures that can work without CONFIG_PCI? I assume their migration
> > > should also break?
> >
> > It's tied to machine-type; the x86 i440fx and q35 machine types have
> > PCI; you can't disable PCI while still having those machine types.
> > (I don't know if you can disable PCI at all on x86)
>
> Ugh, that sounds like we need two machine types on s390x as well
> (s390x-ccw-virtio and s390x-ccw-virtio-nopci or so), built
> conditionally. That whole zpci detanglement is looking worse and
> worse :(
Well fundamentally the migration expects to migrate something into
the same shaped hole on the destination; if you've got a lump of PCI
config on the source there's got to be somewhere for it to fit on the
destination.
Now, if PCI is actually pretty rare; then you might be able to make
the host-pci bridge a normal device and not include it in any
machine type; that way those who want PCI can just instantiate
the host-pci bridge, and those who don't want it just stick with
the base machine type.
Dave
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, (continued)
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/26
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, David Hildenbrand, 2017/09/26
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Yi Min Zhao, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, David Hildenbrand, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Dr. David Alan Gilbert, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/27
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/28
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/28
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/28
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Christian Borntraeger, 2017/09/28
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, Cornelia Huck, 2017/09/28
- Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10, David Hildenbrand, 2017/09/28