Re: [PULL 1/5] hw/pcie-root-port: Fix hotplug for PCI devices requiring IO

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Igor Mammedov <imammedo@redhat.com>
Cc: marcel@redhat.com, "Peter Maydell" <peter.maydell@linaro.org>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	qemu-devel@nongnu.org
Subject: Re: [PULL 1/5] hw/pcie-root-port: Fix hotplug for PCI devices requiring IO
Date: Thu, 30 Sep 2021 06:52:21 -0400	[thread overview]
Message-ID: <20210930065118-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20210930103424.5f408978@redhat.com>

On Thu, Sep 30, 2021 at 10:34:24AM +0200, Igor Mammedov wrote:
> On Wed, 29 Sep 2021 17:47:37 -0400
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Wed, Sep 29, 2021 at 04:41:49PM +0300, Marcel Apfelbaum wrote:
> > > Hi Michael,
> > > 
> > > On Mon, Sep 27, 2021 at 12:49 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > 
> > >     On Mon, Sep 27, 2021 at 10:33:42AM +0100, Daniel P. Berrangé wrote:  
> > >     > On Tue, Aug 03, 2021 at 04:52:03PM -0400, Michael S. Tsirkin wrote:  
> > >     > > From: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> > >     > >
> > >     > > Q35 has now ACPI hotplug enabled by default for PCI(e) devices.
> > >     > > As opposed to native PCIe hotplug, guests like Fedora 34
> > >     > > will not assign IO range to pcie-root-ports not supporting
> > >     > > native hotplug, resulting into a regression.
> > >     > >
> > >     > > Reproduce by:
> > >     > >     qemu-bin -M q35 -device pcie-root-port,id=p1 -monitor stdio
> > >     > >     device_add e1000,bus=p1
> > >     > > In the Guest OS the respective pcie-root-port will have the IO range
> > >     > > disabled.
> > >     > >
> > >     > > Fix it by setting the "reserve-io" hint capability of the
> > >     > > pcie-root-ports so the firmware will allocate the IO range instead.
> > >     > >
> > >     > > Acked-by: Igor Mammedov <imammedo@redhat.com>
> > >     > > Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> > >     > > Message-Id: <20210802090057.1709775-1-marcel@redhat.com>
> > >     > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > >     > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > >     > > ---
> > >     > >  hw/pci-bridge/gen_pcie_root_port.c | 5 +++++
> > >     > >  1 file changed, 5 insertions(+)  
> > >     >
> > >     > This change, when combined with the switch to ACPI based hotplug by
> > >     > default, is responsible for a significant regression in QEMU 6.1.0
> > >     >
> > >     > It is no longer possible to have more than 15 pcie-root-port devices
> > >     > added to a q35 VM in 6.1.0.  Before this I've had as many as 80+ devices
> > >     > present before I stopped trying to add more.
> > >     >
> > >     >   https://gitlab.com/qemu-project/qemu/-/issues/641
> > >     >
> > >     > This regression is significant, because it has broken the out of the
> > >     > box default configuration that OpenStack uses for booting all VMs.
> > >     > They add 16 pcie-root-ports by defalt to allow empty slots for device
> > >     > hotplug under q35 [1].  
> > > 
> > > 
> > >     Indeed, oops. Thanks for the report!
> > > 
> > >     Going back and looking at seabios code, didn't we get confused?
> > >     Shouldn't we have reserved memory and not IO?
> > > 
> > > 
> > > We need the IO space for the legacy PCI bridges, otherwise an empty PCI bridge
> > > will become unusable.  
> > 
> > Maybe we should go back to using OSC then ... the issue
> > is we can't then mix acpi and native hotplug for bridges.
> 
> How OSC could help with the issue?

guests see the pci capability and vonclude that bridge supports hotplug.

> > > 
> > > 
> > >     I see:
> > >                 int resource_optional = pcie_cap && (type ==
> > >     PCI_REGION_TYPE_IO);
> > >                 if (!sum && hotplug_support && !resource_optional)
> > >                     sum = align; /* reserve min size for hot-plug */
> > > 
> > > 
> > >     generally maybe we should just add an ACPI-hotplug capability and
> > >     teach seabios about it?
> > > 
> > > 
> > > I suppose it is possible.
> > > 
> > > Thanks,
> > > Marcel
> > >  
> > > 
> > > 
> > >     Marcel?
> > >   
> > >     > > diff --git a/hw/pci-bridge/gen_pcie_root_port.c b/hw/pci-bridge/  
> > >     gen_pcie_root_port.c  
> > >     > > index ec9907917e..20099a8ae3 100644
> > >     > > --- a/hw/pci-bridge/gen_pcie_root_port.c
> > >     > > +++ b/hw/pci-bridge/gen_pcie_root_port.c
> > >     > > @@ -28,6 +28,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(GenPCIERootPort,  
> > >     GEN_PCIE_ROOT_PORT)  
> > >     > >          (GEN_PCIE_ROOT_PORT_AER_OFFSET + PCI_ERR_SIZEOF)
> > >     > > 
> > >     > >  #define GEN_PCIE_ROOT_PORT_MSIX_NR_VECTOR       1
> > >     > > +#define GEN_PCIE_ROOT_DEFAULT_IO_RANGE          4096
> > >     > > 
> > >     > >  struct GenPCIERootPort {
> > >     > >      /*< private >*/
> > >     > > @@ -75,6 +76,7 @@ static bool gen_rp_test_migrate_msix(void *opaque,  
> > >     int version_id)  
> > >     > >  static void gen_rp_realize(DeviceState *dev, Error **errp)
> > >     > >  {
> > >     > >      PCIDevice *d = PCI_DEVICE(dev);
> > >     > > +    PCIESlot *s = PCIE_SLOT(d);
> > >     > >      GenPCIERootPort *grp = GEN_PCIE_ROOT_PORT(d);
> > >     > >      PCIERootPortClass *rpc = PCIE_ROOT_PORT_GET_CLASS(d);
> > >     > >      Error *local_err = NULL;
> > >     > > @@ -85,6 +87,9 @@ static void gen_rp_realize(DeviceState *dev, Error  
> > >     **errp)  
> > >     > >          return;
> > >     > >      }
> > >     > > 
> > >     > > +    if (grp->res_reserve.io == -1 && s->hotplug && !s->native_hotplug)  
> > >     {  
> > >     > > +        grp->res_reserve.io = GEN_PCIE_ROOT_DEFAULT_IO_RANGE;
> > >     > > +    }
> > >     > >      int rc = pci_bridge_qemu_reserve_cap_init(d, 0,
> > >     > >                                                grp->res_reserve, errp);
> > >     > > 
> > >     > > --
> > >     > > MST
> > >     > >
> > >     > >  
> > >     >
> > >     > Regards,
> > >     > Daniel
> > >     >
> > >     > [1] https://github.com/openstack/tripleo-heat-templates/blob/  
> > >     7a6cd0640ec390a330f5699d8ed60f71b2a9f514/deployment/nova/
> > >     nova-compute-container-puppet.yaml#L462-L472  
> > >     > --
> > >     > |: https://berrange.com      -o-    https://www.flickr.com/photos/  
> > >     dberrange :|  
> > >     > |: https://libvirt.org         -o-            https://  
> > >     fstop138.berrange.com :|  
> > >     > |: https://entangle-photo.org    -o-    https://www.instagram.com/  
> > >     dberrange :|
> > > 
> > >   
> > 