Re: Failure of hot plugging secondary virtio_blk into q35 Windows 2019

[Daniel P . Berrangé]

On Tue, Nov 09, 2021 at 12:01:30PM -0500, Annie.li wrote:
> On 11/9/2021 6:19 AM, Daniel P. Berrangé wrote:
> > On Tue, Nov 09, 2021 at 04:40:10PM +0530, Ani Sinha wrote:
> > > On Tue, Nov 9, 2021 at 3:23 PM Daniel P. Berrangé <berrange@redhat.com> 
> > > wrote:
> > > > On Tue, Nov 09, 2021 at 12:41:39PM +0530, Ani Sinha wrote:
> > > > > +gerd
> > > > > 
> > > > > On Mon, 8 Nov 2021, Annie.li wrote:
> > > > > 
> > > > > > Update:
> > > > > > 
> > > > > > I've tested q35 guest w/o OVMF, the APCI PCI hot-plugging works 
> > > > > > well in q35
> > > > > > guest. Seems this issue only happens in q35 guest w/ OVMF.
> > > > > > 
> > > > > > Looks that there is already a bug filed against this hotplug issue 
> > > > > > in q35
> > > > > > guest w/ OVMF,
> > > > > > 
> > > > > > https://urldefense.com/v3/__https://bugzilla.redhat.com/show_bug.cgi?id=2004829__;!!ACWV5N9M2RV99hQ!bCogoVXfTRaTu03Bg6dQ8NrSINSha4iSSLuZJerOTVdIdWnu1msYwJ8E_c_jRg$
> > > > > > 
> > > > > > In this bug, it is recommended to add "-global
> > > > > > ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off \" on qemu 
> > > > > > command for 6.1.
> > > > > > However, with this option for 6.1(PCIe native hotplug), there still 
> > > > > > are kinds
> > > > > > of issues. For example, one of them is the deleted virtio_blk 
> > > > > > device still
> > > > > > shows in the Device Manager in Windows q35 guest, the operation of 
> > > > > > re-scanning
> > > > > > new hardware takes forever there. This means both PCIe native 
> > > > > > hotplug and ACPI
> > > > > > hotplug all have issues in q35 guests.
> > > > > This is sad.
> > > > > 
> > > > > > Per comments in this bug, changes in both OVMF and QEMU are 
> > > > > > necessary to
> > > > > > support ACPI hot plug in q35 guest. The fixes may likely be 
> > > > > > available in QEMU
> > > > > > 6.2.0.
> > > > > So we are in soft code freeze for 6.2:
> > > > > https://urldefense.com/v3/__https://wiki.qemu.org/Planning/6.2__;!!ACWV5N9M2RV99hQ!bCogoVXfTRaTu03Bg6dQ8NrSINSha4iSSLuZJerOTVdIdWnu1msYwJ_pKO8AzA$
> > > > > 
> > > > > I am curious about Gerd's comment #10:
> > > > > "The 6.2 rebase should make hotplug work
> > > > > again with the default configuration."
> > > > > 
> > > > > Sadly I have not seen any public discussion on what we want to do
> > > > > for the issues with acpi hotplug for bridges in q35.
> > > > I've raised one of the problems a week ago and there's a promised
> > > > fix
> > > > 
> > > >   
> > > > https://urldefense.com/v3/__https://lists.gnu.org/archive/html/qemu-devel/2021-11/msg00558.html__;!!ACWV5N9M2RV99hQ!bCogoVXfTRaTu03Bg6dQ8NrSINSha4iSSLuZJerOTVdIdWnu1msYwJ-np8GcUA$
> > > So 
> > > https://urldefense.com/v3/__https://gitlab.com/qemu-project/qemu/-/issues/641__;!!ACWV5N9M2RV99hQ!bCogoVXfTRaTu03Bg6dQ8NrSINSha4iSSLuZJerOTVdIdWnu1msYwJ86xk2gtg$
> > >   is the same as
> > > https://urldefense.com/v3/__https://bugzilla.redhat.com/show_bug.cgi?id=2006409__;!!ACWV5N9M2RV99hQ!bCogoVXfTRaTu03Bg6dQ8NrSINSha4iSSLuZJerOTVdIdWnu1msYwJ9crT9JKw$
> > > 
> > > isn't it?
> > Yes, one upstream, one downstream.
> 
> Thanks for the info.
> 
> So q35 guests with either OVMF or SeaBIOS have different ACPI hotplug issues
> in QEMU 6.1.
> 
> As Ani mentioned earlier, QEMU 6.2 is in soft code freeze.
> Today(Nov 9) is the date of hard feature freeze.
> 
> I suppose this means the fix for the issue with SeaBIOS or the feature to
> cooperate
> with the coming change in OVMF won't happen in 6.2?

Patches are allowed if they're bug fixes. If a change requires coordination
with an OVMF change too though, I think that's going to be difficult to
justify. 

Our fallback option is to revert to native hotplug out of the box for
QEMU machine types in 6.2

Regards,
Daniel
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