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Re: [RFC PATCH v3 16/31] hw/pci: Plumb _UID through host bridges
From: |
Michael S. Tsirkin |
Subject: |
Re: [RFC PATCH v3 16/31] hw/pci: Plumb _UID through host bridges |
Date: |
Tue, 2 Feb 2021 10:51:55 -0500 |
On Tue, Feb 02, 2021 at 07:42:57AM -0800, Ben Widawsky wrote:
> Thanks for looking! Mixing comments to Jonathan and Michael..
>
> On 21-02-02 10:24:43, Michael S. Tsirkin wrote:
> > On Tue, Feb 02, 2021 at 03:00:56PM +0000, Jonathan Cameron wrote:
> > > On Mon, 1 Feb 2021 16:59:33 -0800
> > > Ben Widawsky <ben.widawsky@intel.com> wrote:
> > >
> > > > Currently, QEMU makes _UID equivalent to the bus number (_BBN). While
> > > > there is nothing wrong with doing it this way, CXL spec has a heavy
> > > > reliance on _UID to identify host bridges and there is no link to the
> > > > bus number. Having a distinct UID solves two problems. The first is it
> > > > gets us around the limitation of 256 (current max bus number).
> >
> > Not sure I understand. You want more than 256 host bridges?
> >
>
> I don't want more than 256 host bridges, but I want the ability to
> disaggregate
> _UID and bus (_BBN). The reasoning is just to align with the spec where _UID
> is
> used to identify a CXL host bridge which is unrelated (perhaps) to the bus
> number.
Which spec is that?
> > > The
> > > > second is it allows us to replicate hardware configurations where bus
> > > > number and uid aren't equivalent.
> >
> > A bit more data on when this needs to be the case?
> >
>
> Doesn't *need* to be the case. I was making a concerted effort to allow full
> spec flexibility, but I don't believe it to be necessary unless we want to
> accurately emulate a real platform.
>
> > > The latter has benefits for our
> > > > development and debugging using QEMU.
> > > >
> > > > The other way to do this would be to implement the expanded bus
> > > > numbering, but having an explicit uid makes more sense when trying to
> > > > replicate real hardware configurations.
> > > >
> > > > The QEMU commandline to utilize this would be:
> > > > -device pxb-cxl,id=cxl.0,bus="pcie.0",bus_nr=1,uid=x
> > > >
> > > > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> >
> > However, if doing this how do we ensure UID is still unique?
> > What do we do for cases where UID was not specified?
> > One idea is to generate a string UID and just stick the bus #
> > in there.
>
> This is totally mishandled in the code currently. I like your idea though.
>
> >
> >
> > > > --
> > > >
> > > > I'm guessing this patch will be somewhat controversial. For early CXL
> > > > work, this can be dropped without too much heartache.
> > >
> > > Whilst I'm not personally against, this maybe best to drop for now as you
> > > say.
> > >
>
> I think it'd be good to understand from the PCIe experts if CXL matches in
> this
> regard. If PCIe generally allows (and does in practice) _UID not matching
> _BBN,
> perhaps this is an overall improvement to the code.
Well
6.1.12 _UID (Unique ID)
This object provides OSPM with a logical device ID that does not change
across reboots. This object
is optional, but is required when the device has no other way to report
a persistent unique device ID.
The _UID must be unique across all devices with either a common _HID or
_CID. This is because a
device needs to be uniquely identified to the OSPM, which may match on
either a _HID or a _CID to
identify the device. The uniqueness match must be true regardless of
whether the OSPM uses the
_HID or the _CID. OSPM typically uses the unique device ID to ensure
that the device-specific
information, such as network protocol binding information, is
remembered for the device even if its
relative location changes. For most integrated devices, this object
contains a unique identifier.
A _UID object evaluates to either a numeric value or a string.
IOW _UID is there so guest can tell devices with identical HID/CID apart.
> > > > ---
> > > > hw/i386/acpi-build.c | 3 ++-
> > > > hw/pci-bridge/pci_expander_bridge.c | 19 +++++++++++++++++++
> > > > hw/pci/pci.c | 11 +++++++++++
> > > > include/hw/pci/pci.h | 1 +
> > > > include/hw/pci/pci_bus.h | 1 +
> > > > 5 files changed, 34 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > > > index cf6eb54c22..145a503e92 100644
> > > > --- a/hw/i386/acpi-build.c
> > > > +++ b/hw/i386/acpi-build.c
> > > > @@ -1343,6 +1343,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> > > > QLIST_FOREACH(bus, &bus->child, sibling) {
> > > > uint8_t bus_num = pci_bus_num(bus);
> > > > uint8_t numa_node = pci_bus_numa_node(bus);
> > > > + int32_t uid = pci_bus_uid(bus);
> > > >
> > > > /* look only for expander root buses */
> > > > if (!pci_bus_is_root(bus)) {
> > > > @@ -1356,7 +1357,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> > > > scope = aml_scope("\\_SB");
> > > > dev = aml_device("PC%.02X", bus_num);
> > > > aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
> > > > - init_pci_acpi(dev, bus_num, pci_bus_is_express(bus) ? PCIE
> > > > : PCI);
> > > > + init_pci_acpi(dev, uid, pci_bus_is_express(bus) ? PCIE :
> > > > PCI);
> > > >
> > > > if (numa_node != NUMA_NODE_UNASSIGNED) {
> > > > aml_append(dev, aml_name_decl("_PXM",
> > > > aml_int(numa_node)));
> > > > diff --git a/hw/pci-bridge/pci_expander_bridge.c
> > > > b/hw/pci-bridge/pci_expander_bridge.c
> > > > index b42592e1ff..5021b60435 100644
> > > > --- a/hw/pci-bridge/pci_expander_bridge.c
> > > > +++ b/hw/pci-bridge/pci_expander_bridge.c
> > > > @@ -67,6 +67,7 @@ struct PXBDev {
> > > >
> > > > uint8_t bus_nr;
> > > > uint16_t numa_node;
> > > > + int32_t uid;
> > > > };
> > > >
> > > > static PXBDev *convert_to_pxb(PCIDevice *dev)
> >
> > As long as we are doing this, do we want to support a string uid too?
> > How about a 64 bit uid? Why not?
>
> If generally the idea of the patch is welcome, I am happy to change it.
I am still not sure, let's figure out the motivation.
For example, grep for UID and you will find more cases
like this. E.g. hw/pci-host/gpex-acpi.c
Do we care?
> >
> >
> > > > @@ -98,12 +99,20 @@ static uint16_t pxb_bus_numa_node(PCIBus *bus)
> > > > return pxb->numa_node;
> > > > }
> > > >
> > > > +static int32_t pxb_bus_uid(PCIBus *bus)
> > > > +{
> > > > + PXBDev *pxb = convert_to_pxb(bus->parent_dev);
> > > > +
> > > > + return pxb->uid;
> > > > +}
> > > > +
> > > > static void pxb_bus_class_init(ObjectClass *class, void *data)
> > > > {
> > > > PCIBusClass *pbc = PCI_BUS_CLASS(class);
> > > >
> > > > pbc->bus_num = pxb_bus_num;
> > > > pbc->numa_node = pxb_bus_numa_node;
> > > > + pbc->uid = pxb_bus_uid;
> > > > }
> > > >
> > > > static const TypeInfo pxb_bus_info = {
> > > > @@ -329,6 +338,7 @@ static Property pxb_dev_properties[] = {
> > > > /* Note: 0 is not a legal PXB bus number. */
> > > > DEFINE_PROP_UINT8("bus_nr", PXBDev, bus_nr, 0),
> > > > DEFINE_PROP_UINT16("numa_node", PXBDev, numa_node,
> > > > NUMA_NODE_UNASSIGNED),
> > > > + DEFINE_PROP_INT32("uid", PXBDev, uid, -1),
> > > > DEFINE_PROP_END_OF_LIST(),
> > > > };
> > > >
> > > > @@ -400,12 +410,21 @@ static const TypeInfo pxb_pcie_dev_info = {
> > > >
> > > > static void pxb_cxl_dev_realize(PCIDevice *dev, Error **errp)
> > > > {
> > > > + PXBDev *pxb = convert_to_pxb(dev);
> > > > +
> > > > /* A CXL PXB's parent bus is still PCIe */
> > > > if (!pci_bus_is_express(pci_get_bus(dev))) {
> > > > error_setg(errp, "pxb-cxl devices cannot reside on a PCI bus");
> > > > return;
> > > > }
> > > >
> > > > + if (pxb->uid < 0) {
> > > > + error_setg(errp, "pxb-cxl devices must have a valid uid
> > > > (0-2147483647)");
> > > > + return;
> > > > + }
> > > > +
> > > > + /* FIXME: Check that uid doesn't collide with UIDs of other host
> > > > bridges */
> > > > +
> > > > pxb_dev_realize_common(dev, CXL, errp);
> > > > }
> > > >
> > > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > > > index adbe8aa260..bf019d91a0 100644
> > > > --- a/hw/pci/pci.c
> > > > +++ b/hw/pci/pci.c
> > > > @@ -170,6 +170,11 @@ static uint16_t pcibus_numa_node(PCIBus *bus)
> > > > return NUMA_NODE_UNASSIGNED;
> > > > }
> > > >
> > > > +static int32_t pcibus_uid(PCIBus *bus)
> > > > +{
> > > > + return -1;
> > > > +}
> > > > +
> > > > static void pci_bus_class_init(ObjectClass *klass, void *data)
> > > > {
> > > > BusClass *k = BUS_CLASS(klass);
> > > > @@ -184,6 +189,7 @@ static void pci_bus_class_init(ObjectClass *klass,
> > > > void *data)
> > > >
> > > > pbc->bus_num = pcibus_num;
> > > > pbc->numa_node = pcibus_numa_node;
> > > > + pbc->uid = pcibus_uid;
> > > > }
> > > >
> > > > static const TypeInfo pci_bus_info = {
> > > > @@ -530,6 +536,11 @@ int pci_bus_numa_node(PCIBus *bus)
> > > > return PCI_BUS_GET_CLASS(bus)->numa_node(bus);
> > > > }
> > > >
> > > > +int pci_bus_uid(PCIBus *bus)
> > > > +{
> > > > + return PCI_BUS_GET_CLASS(bus)->uid(bus);
> > > > +}
> > > > +
> > > > static int get_pci_config_device(QEMUFile *f, void *pv, size_t size,
> > > > const VMStateField *field)
> > > > {
> > > > diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> > > > index bde3697bee..a46de48ccd 100644
> > > > --- a/include/hw/pci/pci.h
> > > > +++ b/include/hw/pci/pci.h
> > > > @@ -463,6 +463,7 @@ static inline int pci_dev_bus_num(const PCIDevice
> > > > *dev)
> > > > }
> > > >
> > > > int pci_bus_numa_node(PCIBus *bus);
> > > > +int pci_bus_uid(PCIBus *bus);
> > > > void pci_for_each_device(PCIBus *bus, int bus_num,
> > > > void (*fn)(PCIBus *bus, PCIDevice *d, void
> > > > *opaque),
> > > > void *opaque);
> > > > diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
> > > > index eb94e7e85c..3c9fbc55bb 100644
> > > > --- a/include/hw/pci/pci_bus.h
> > > > +++ b/include/hw/pci/pci_bus.h
> > > > @@ -17,6 +17,7 @@ struct PCIBusClass {
> > > >
> > > > int (*bus_num)(PCIBus *bus);
> > > > uint16_t (*numa_node)(PCIBus *bus);
> > > > + int32_t (*uid)(PCIBus *bus);
> > > > };
> > > >
> > > > enum PCIBusFlags {
> >
- [RFC PATCH v3 13/31] qtest: allow DSDT acpi table changes, (continued)
- [RFC PATCH v3 13/31] qtest: allow DSDT acpi table changes, Ben Widawsky, 2021/02/01
- [RFC PATCH v3 11/31] hw/pci/cxl: Create a CXL bus type, Ben Widawsky, 2021/02/01
- [RFC PATCH v3 12/31] hw/pxb: Allow creation of a CXL PXB (host bridge), Ben Widawsky, 2021/02/01
- [RFC PATCH v3 14/31] acpi/pci: Consolidate host bridge setup, Ben Widawsky, 2021/02/01
- [RFC PATCH v3 15/31] tests/acpi: remove stale allowed tables, Ben Widawsky, 2021/02/01
- [RFC PATCH v3 16/31] hw/pci: Plumb _UID through host bridges, Ben Widawsky, 2021/02/01
[RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Ben Widawsky, 2021/02/01
- Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Jonathan Cameron, 2021/02/02
- Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Ben Widawsky, 2021/02/02
- Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Jonathan Cameron, 2021/02/02
- Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Ben Widawsky, 2021/02/02
- Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142), Jonathan Cameron, 2021/02/02
[RFC PATCH v3 18/31] acpi/pxb/cxl: Reserve host bridge MMIO, Ben Widawsky, 2021/02/01
[RFC PATCH v3 19/31] hw/pxb/cxl: Add "windows" for host bridges, Ben Widawsky, 2021/02/01
[RFC PATCH v3 20/31] hw/cxl/rp: Add a root port, Ben Widawsky, 2021/02/01