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Re: [PULL 1/5] hw/pcie-root-port: Fix hotplug for PCI devices requiring
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [PULL 1/5] hw/pcie-root-port: Fix hotplug for PCI devices requiring IO |
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Date: |
Thu, 30 Sep 2021 06:52:21 -0400 |
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 :|
> > >
> > >
> >