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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 2/2] pci: allow slot_reserved_mask to be ignored with manual slot assignment
On 3/14/2023 9:17 AM, Michael S. Tsirkin wrote:
> On Tue, Mar 14, 2023 at 12:43:12PM +0000, Mark Cave-Ayland wrote:
> > On 14/03/2023 06:33, Michael S. Tsirkin wrote:
> >
> > > On Tue, Mar 14, 2023 at 12:01:09AM -0400, Chuck Zmudzinski wrote:
> > > > Commit 4f67543bb8c5 ("xen/pt: reserve PCI slot 2 for Intel
> > > > igd-passthru")
> > > > uses slot_reserved_mask to reserve slot 2 for the Intel IGD for the
> > > > xenfv machine when the guest is configured for igd-passthru.
> > > >
> > > > A desired extension to that commit is to allow use of the reserved slot
> > > > if the administrator manually configures a device to use the reserved
> > > > slot. Currently, slot_reserved_mask is enforced unconditionally. With
> > > > this patch, the pci bus can be configured so the slot is only reserved
> > > > if the pci device to be added to the bus is configured for automatic
> > > > slot assignment.
> > > >
> > > > To enable the desired behavior of slot_reserved_mask machine, add a
> > > > boolean member enforce_slot_reserved_mask_manual to struct PCIBus and
> > > > add a function pci_bus_ignore_slot_reserved_mask_manual which can be
> > > > called to change the default behavior of always enforcing
> > > > slot_reserved_mask so, in that case, slot_reserved_mask is only enforced
> > > > when the pci device being added is configured for automatic slot
> > > > assignment.
> > > >
> > > > Call the new pci_bus_ignore_slot_reserved_mask_manual function after
> > > > creating the pci bus for the pc/i440fx/xenfv machine type to implement
> > > > the desired behavior of causing slot_reserved_mask to only apply when
> > > > the pci device to be added to a pc/i440fx/xenfv machine is configured
> > > > for automatic slot assignment.
> > > >
> > > > Link:
> > > > https://lore.kernel.org/qemu-devel/20230106064838-mutt-send-email-mst@xxxxxxxxxx/
> > > > Signed-off-by: Chuck Zmudzinski <brchuckz@xxxxxxx>
> > >
> > > I really dislike this.
> > > It seems that xen should not have used slot_reserved_mask,
> > > and instead needs something new like slot_manual_mask.
> > > No?
> >
> > My suggestion was to move the validation logic to a separate callback
> > function in PCIBus (see
> > https://lists.gnu.org/archive/html/qemu-devel/2023-03/msg03988.html) but
> > perhaps I wasn't clear enough in pointing out that I was thinking this could
> > *replace* the existing slot_reserved_mask mechanism, rather than providing a
> > hook to allow it to be manipulated.
> >
> > Here's a very rough patch put together over lunch that attempts this for
> > pci_bus_devfn_reserved(): the idea is that sun4u and Xen would call
> > pci_bus_set_slot_reserved_fn() with a suitable pci_slot_reserved_fn
> > implementation, and slot_reserved_mask gets removed completely i.e.:
> >
> >
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index def5000e7b..30b856499a 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -493,6 +493,13 @@ bool pci_bus_bypass_iommu(PCIBus *bus)
> > return host_bridge->bypass_iommu;
> > }
> >
> > +static bool pci_bus_default_slot_reserved(PCISlotReservationType restype,
> > + int devfn)
> > +{
> > + /* All slots accessible by default */
> > + return false;
> > +}
> > +
> > static void pci_root_bus_internal_init(PCIBus *bus, DeviceState *parent,
> > MemoryRegion *address_space_mem,
> > MemoryRegion *address_space_io,
> > @@ -500,7 +507,7 @@ static void pci_root_bus_internal_init(PCIBus *bus,
> > DeviceState *parent,
> > {
> > assert(PCI_FUNC(devfn_min) == 0);
> > bus->devfn_min = devfn_min;
> > - bus->slot_reserved_mask = 0x0;
> > + bus->slot_reserved_fn = pci_bus_default_slot_reserved;
> > bus->address_space_mem = address_space_mem;
> > bus->address_space_io = address_space_io;
> > bus->flags |= PCI_BUS_IS_ROOT;
> > @@ -1111,9 +1118,15 @@ static bool pci_bus_devfn_available(PCIBus *bus, int
> > devfn)
> > return !(bus->devices[devfn]);
> > }
> >
> > -static bool pci_bus_devfn_reserved(PCIBus *bus, int devfn)
> > +static bool pci_bus_devfn_reserved(PCIBus *bus, int devfn,
> > + PCISlotReservationType restype)
> > +{
> > + return bus->slot_reserved_fn(restype, devfn);
> > +}
> > +
> > +void pci_bus_set_slot_reserved_fn(PCIBus *bus, pci_slot_reserved_fn fn)
> > {
> > - return bus->slot_reserved_mask & (1UL << PCI_SLOT(devfn));
> > + bus->slot_reserved_fn = fn;
> > }
> >
> > /* -1 for devfn means auto assign */
> > @@ -1141,7 +1154,7 @@ static PCIDevice *do_pci_register_device(PCIDevice
> > *pci_dev,
> > for(devfn = bus->devfn_min ; devfn < ARRAY_SIZE(bus->devices);
> > devfn += PCI_FUNC_MAX) {
> > if (pci_bus_devfn_available(bus, devfn) &&
> > - !pci_bus_devfn_reserved(bus, devfn)) {
> > + !pci_bus_devfn_reserved(bus, devfn,
> > PCI_SLOT_RESERVATION_AUTO)) {
> > goto found;
> > }
> > }
> > @@ -1149,7 +1162,7 @@ static PCIDevice *do_pci_register_device(PCIDevice
> > *pci_dev,
> > "or reserved", name);
> > return NULL;
> > found: ;
> > - } else if (pci_bus_devfn_reserved(bus, devfn)) {
> > + } else if (pci_bus_devfn_reserved(bus, devfn,
> > PCI_SLOT_RESERVATION_MANUAL)) {
> > error_setg(errp, "PCI: slot %d function %d not available for %s,"
> > MemoryRegion *address_space_io,
> > @@ -500,7 +507,7 @@ static void pci_root_bus_internal_init(PCIBus *bus,
> > DeviceState *parent,
> > {
> > assert(PCI_FUNC(devfn_min) == 0);
> > bus->devfn_min = devfn_min;
> > - bus->slot_reserved_mask = 0x0;
> > + bus->slot_reserved_fn = pci_bus_default_slot_reserved;
> > bus->address_space_mem = address_space_mem;
> > bus->address_space_io = address_space_io;
> > bus->flags |= PCI_BUS_IS_ROOT;
> > @@ -1111,9 +1118,15 @@ static bool pci_bus_devfn_available(PCIBus *bus, int
> > devfn)
> > return !(bus->devices[devfn]);
> > }
> >
> > -static bool pci_bus_devfn_reserved(PCIBus *bus, int devfn)
> > +static bool pci_bus_devfn_reserved(PCIBus *bus, int devfn,
> > + PCISlotReservationType restype)
> > +{
> > + return bus->slot_reserved_fn(restype, devfn);
> > +}
> > +
> > +void pci_bus_set_slot_reserved_fn(PCIBus *bus, pci_slot_reserved_fn fn)
> > {
> > - return bus->slot_reserved_mask & (1UL << PCI_SLOT(devfn));
> > + bus->slot_reserved_fn = fn;
> > }
> >
> > /* -1 for devfn means auto assign */
> > @@ -1141,7 +1154,7 @@ static PCIDevice *do_pci_register_device(PCIDevice
> > *pci_dev,
> > for(devfn = bus->devfn_min ; devfn < ARRAY_SIZE(bus->devices);
> > devfn += PCI_FUNC_MAX) {
> > if (pci_bus_devfn_available(bus, devfn) &&
> > - !pci_bus_devfn_reserved(bus, devfn)) {
> > + !pci_bus_devfn_reserved(bus, devfn,
> > PCI_SLOT_RESERVATION_AUTO)) {
> > goto found;
> > }
> > }
> > @@ -1149,7 +1162,7 @@ static PCIDevice *do_pci_register_device(PCIDevice
> > *pci_dev,
> > "or reserved", name);
> > return NULL;
> > found: ;
> > - } else if (pci_bus_devfn_reserved(bus, devfn)) {
> > + } else if (pci_bus_devfn_reserved(bus, devfn,
> > PCI_SLOT_RESERVATION_MANUAL)) {
> > error_setg(errp, "PCI: slot %d function %d not available for %s,"
> > " reserved",
> > PCI_SLOT(devfn), PCI_FUNC(devfn), name);
> > diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> > index d5a40cd058..8a949f7ae1 100644
> > --- a/include/hw/pci/pci.h
> > +++ b/include/hw/pci/pci.h
> > @@ -257,10 +257,18 @@ MemoryRegion *pci_address_space_io(PCIDevice *dev);
> > */
> > int pci_bar(PCIDevice *d, int reg);
> >
> > +typedef enum PCISlotReservationType {
> > + PCI_SLOT_RESERVATION_AUTO,
> > + PCI_SLOT_RESERVATION_MANUAL
> > +} PCISlotReservationType;
> > +
> > +typedef bool (*pci_slot_reserved_fn)(PCISlotReservationType restype, int
> > devfn);
> > typedef void (*pci_set_irq_fn)(void *opaque, int irq_num, int level);
> > typedef int (*pci_map_irq_fn)(PCIDevice *pci_dev, int irq_num);
> > typedef PCIINTxRoute (*pci_route_irq_fn)(void *opaque, int pin);
> >
> > +void pci_bus_set_slot_reserved_fn(PCIBus *bus, pci_slot_reserved_fn fn);
> > +
> > #define TYPE_PCI_BUS "PCI"
> > OBJECT_DECLARE_TYPE(PCIBus, PCIBusClass, PCI_BUS)
> > #define TYPE_PCIE_BUS "PCIE"
> > diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
> > index 5653175957..d68ea1418d 100644
> > --- a/include/hw/pci/pci_bus.h
> > +++ b/include/hw/pci/pci_bus.h
> > @@ -36,7 +36,7 @@ struct PCIBus {
> > PCIIOMMUFunc iommu_fn;
> > void *iommu_opaque;
> > uint8_t devfn_min;
> > - uint32_t slot_reserved_mask;
> > + pci_slot_reserved_fn slot_reserved_fn;
> > pci_set_irq_fn set_irq;
> > pci_map_irq_fn map_irq;
> > pci_route_irq_fn route_intx_to_irq;
> >
> >
> > If this approach seems reasonable, I'm happy for someone else to take this
> > over and turn it into a proper series.
> >
> >
> > ATB,
> >
> > Mark.
>
> It's ok too though I think I like chuck's proposal better:
> less callbacks to chase.
>
I would be willing to pursue this if there were more use cases for
slot_reserved_mask than just the two cases we have now: xen and sun4u.
Until there is a clear demand for a more general way to manipulate the
mask, I agree with Michael that the KISS principle should apply here.
Kind regards,
Chuck
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