Re: [PATCH v8] xen/pt: reserve PCI slot 2 for Intel igd-passthru

[Bernhard Beschow <shentey@xxxxxxxxx>]

Am 11. Januar 2023 15:40:24 UTC schrieb Chuck Zmudzinski <brchuckz@xxxxxxx>:
>On 1/10/23 3:16 AM, Michael S. Tsirkin wrote:
>> On Tue, Jan 10, 2023 at 02:08:34AM -0500, Chuck Zmudzinski wrote:
>>> Intel specifies that the Intel IGD must occupy slot 2 on the PCI bus,
>>> as noted in docs/igd-assign.txt in the Qemu source code.
>>> 
>>> Currently, when the xl toolstack is used to configure a Xen HVM guest with
>>> Intel IGD passthrough to the guest with the Qemu upstream device model,
>>> a Qemu emulated PCI device will occupy slot 2 and the Intel IGD will occupy
>>> a different slot. This problem often prevents the guest from booting.
>>> 
>>> The only available workaround is not good: Configure Xen HVM guests to use
>>> the old and no longer maintained Qemu traditional device model available
>>> from xenbits.xen.org which does reserve slot 2 for the Intel IGD.
>>> 
>>> To implement this feature in the Qemu upstream device model for Xen HVM
>>> guests, introduce the following new functions, types, and macros:
>>> 
>>> * XEN_PT_DEVICE_CLASS declaration, based on the existing TYPE_XEN_PT_DEVICE
>>> * XEN_PT_DEVICE_GET_CLASS macro helper function for XEN_PT_DEVICE_CLASS
>>> * typedef XenPTQdevRealize function pointer
>>> * XEN_PCI_IGD_SLOT_MASK, the value of slot_reserved_mask to reserve slot 2
>>> * xen_igd_reserve_slot and xen_igd_clear_slot functions
>>> 
>>> The new xen_igd_reserve_slot function uses the existing slot_reserved_mask
>>> member of PCIBus to reserve PCI slot 2 for Xen HVM guests configured using
>>> the xl toolstack with the gfx_passthru option enabled, which sets the
>>> igd-passthru=on option to Qemu for the Xen HVM machine type.
>>> 
>>> The new xen_igd_reserve_slot function also needs to be implemented in
>>> hw/xen/xen_pt_stub.c to prevent FTBFS during the link stage for the case
>>> when Qemu is configured with --enable-xen and --disable-xen-pci-passthrough,
>>> in which case it does nothing.
>>> 
>>> The new xen_igd_clear_slot function overrides qdev->realize of the parent
>>> PCI device class to enable the Intel IGD to occupy slot 2 on the PCI bus
>>> since slot 2 was reserved by xen_igd_reserve_slot when the PCI bus was
>>> created in hw/i386/pc_piix.c for the case when igd-passthru=on.
>>> 
>>> Move the call to xen_host_pci_device_get, and the associated error
>>> handling, from xen_pt_realize to the new xen_igd_clear_slot function to
>>> initialize the device class and vendor values which enables the checks for
>>> the Intel IGD to succeed. The verification that the host device is an
>>> Intel IGD to be passed through is done by checking the domain, bus, slot,
>>> and function values as well as by checking that gfx_passthru is enabled,
>>> the device class is VGA, and the device vendor in Intel.
>>> 
>>> Signed-off-by: Chuck Zmudzinski <brchuckz@xxxxxxx>
>>> ---
>>> Notes that might be helpful to reviewers of patched code in hw/xen:
>>> 
>>> The new functions and types are based on recommendations from Qemu docs:
>>> https://qemu.readthedocs.io/en/latest/devel/qom.html
>>> 
>>> Notes that might be helpful to reviewers of patched code in hw/i386:
>>> 
>>> The small patch to hw/i386/pc_piix.c is protected by CONFIG_XEN so it does
>>> not affect builds that do not have CONFIG_XEN defined.
>>> 
>>> xen_igd_gfx_pt_enabled() in the patched hw/i386/pc_piix.c file is an
>>> existing function that is only true when Qemu is built with
>>> xen-pci-passthrough enabled and the administrator has configured the Xen
>>> HVM guest with Qemu's igd-passthru=on option.
>>> 
>>> v2: Remove From: <email address> tag at top of commit message
>>> 
>>> v3: Changed the test for the Intel IGD in xen_igd_clear_slot:
>>> 
>>>     if (is_igd_vga_passthrough(&s->real_device) &&
>>>         (s->real_device.vendor_id == PCI_VENDOR_ID_INTEL)) {
>>> 
>>>     is changed to
>>> 
>>>     if (xen_igd_gfx_pt_enabled() && (s->hostaddr.slot == 2)
>>>         && (s->hostaddr.function == 0)) {
>>> 
>>>     I hoped that I could use the test in v2, since it matches the
>>>     other tests for the Intel IGD in Qemu and Xen, but those tests
>>>     do not work because the necessary data structures are not set with
>>>     their values yet. So instead use the test that the administrator
>>>     has enabled gfx_passthru and the device address on the host is
>>>     02.0. This test does detect the Intel IGD correctly.
>>> 
>>> v4: Use brchuckz@xxxxxxx instead of brchuckz@xxxxxxxxxxxx for the author's
>>>     email address to match the address used by the same author in commits
>>>     be9c61da and c0e86b76
>>>     
>>>     Change variable for XEN_PT_DEVICE_CLASS: xptc changed to xpdc
>>> 
>>> v5: The patch of xen_pt.c was re-worked to allow a more consistent test
>>>     for the Intel IGD that uses the same criteria as in other places.
>>>     This involved moving the call to xen_host_pci_device_get from
>>>     xen_pt_realize to xen_igd_clear_slot and updating the checks for the
>>>     Intel IGD in xen_igd_clear_slot:
>>>     
>>>     if (xen_igd_gfx_pt_enabled() && (s->hostaddr.slot == 2)
>>>         && (s->hostaddr.function == 0)) {
>>> 
>>>     is changed to
>>> 
>>>     if (is_igd_vga_passthrough(&s->real_device) &&
>>>         s->real_device.domain == 0 && s->real_device.bus == 0 &&
>>>         s->real_device.dev == 2 && s->real_device.func == 0 &&
>>>         s->real_device.vendor_id == PCI_VENDOR_ID_INTEL) {
>>> 
>>>     Added an explanation for the move of xen_host_pci_device_get from
>>>     xen_pt_realize to xen_igd_clear_slot to the commit message.
>>> 
>>>     Rebase.
>>> 
>>> v6: Fix logging by removing these lines from the move from xen_pt_realize
>>>     to xen_igd_clear_slot that was done in v5:
>>> 
>>>     XEN_PT_LOG(d, "Assigning real physical device %02x:%02x.%d"
>>>                " to devfn 0x%x\n",
>>>                s->hostaddr.bus, s->hostaddr.slot, s->hostaddr.function,
>>>                s->dev.devfn);
>>> 
>>>     This log needs to be in xen_pt_realize because s->dev.devfn is not
>>>     set yet in xen_igd_clear_slot.
>>> 
>>> v7: The v7 that was posted to the mailing list was incorrect. v8 is what
>>>     v7 was intended to be.
>>> 
>>> v8: Inhibit out of context log message and needless processing by
>>>     adding 2 lines at the top of the new xen_igd_clear_slot function:
>>> 
>>>     if (!(pci_bus->slot_reserved_mask & XEN_PCI_IGD_SLOT_MASK))
>>>         return;
>>> 
>>>     Rebase. This removed an unnecessary header file from xen_pt.h 
>>> 
>>>  hw/i386/pc_piix.c    |  3 +++
>>>  hw/xen/xen_pt.c      | 49 ++++++++++++++++++++++++++++++++++++--------
>>>  hw/xen/xen_pt.h      | 16 +++++++++++++++
>>>  hw/xen/xen_pt_stub.c |  4 ++++
>>>  4 files changed, 63 insertions(+), 9 deletions(-)
>>> 
>>> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>>> index b48047f50c..bc5efa4f59 100644
>>> --- a/hw/i386/pc_piix.c
>>> +++ b/hw/i386/pc_piix.c
>>> @@ -405,6 +405,9 @@ static void pc_xen_hvm_init(MachineState *machine)
>>>      }
>>>  
>>>      pc_xen_hvm_init_pci(machine);
>>> +    if (xen_igd_gfx_pt_enabled()) {
>>> +        xen_igd_reserve_slot(pcms->bus);
>>> +    }
>>>      pci_create_simple(pcms->bus, -1, "xen-platform");
>>>  }
>>>  #endif
>> 
>> I would even maybe go further and move the whole logic into
>> xen_igd_reserve_slot. And I would even just name it
>> xen_hvm_init_reserved_slots without worrying about the what
>> or why at the pc level.  At this point it will be up to Xen maintainers.
>
>I see to do that would be to resolve the two pc_xen_hvm*
>functions in pc_piix.c that are guarded by CONFIG_XEN and
>move them to an appropriate place such as xen-hvm.c.
>
>That is along the lines of the work that Bernhard and Philippe
>are doing, so I am Cc'ing them. My first inclination is just
>to defer to them: I think eventually the little patch I propose
>here to pc_piix.c is eventually going to be moved out of pc_piix.c
>by Bernhard in a future patch.
>
>What they have been doing is very conservative, and I expect
>if and when Bernhard gets here to resolve those functions, they
>will do it in a way that keeps the dependency of the xenfv machine
>type on the pc machine type and the pc_init1 function.
>
>What I would propose would be to break the dependency of xenfv
>on the pc_init1 function. That is, I would propose having a
>xenfv_init function in xen-hvm.c, and the first version would
>be the current version of pc_init1, so xenfv would still depend
>on many i440fx type things, but with the change xen developers
>would be free to tweak xenfv_init without affecting the users
>of the pc machine type.
>
>Would that be a good idea? If I get posiive feedback for this
>idea, I will put it on the table, probably initially as an RFC
>patch.

In various patches I've been decoupling 1/ PIIX3 from Xen and 2/ QEMU's Xen 
integration code from the PC machine. My idea is to confine all wiring for a 
PIIX based PC machine using Xen in pc_piix.c. The pc_xen_hvm* functions seem to 
do exactly that, so I'd leave them there, at least for now.

What I would like to avoid is for the Xen integration code to make assumptions 
that an x86 or PC machine is always based on i440fx or PIIX3.

I like Michael's idea of going one step further, both in terms of the approach 
and the reasoning.

Best regards,
Bernhard

>Also, thanks, Michael, for your other suggestions for this patch
>about using macros for the devfn constants.
>
>Chuck
>
>> 
>>> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
>>> index 0ec7e52183..eff38155ef 100644
>>> --- a/hw/xen/xen_pt.c
>>> +++ b/hw/xen/xen_pt.c
>>> @@ -780,15 +780,6 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
>>>                 s->hostaddr.bus, s->hostaddr.slot, s->hostaddr.function,
>>>                 s->dev.devfn);
>>>  
>>> -    xen_host_pci_device_get(&s->real_device,
>>> -                            s->hostaddr.domain, s->hostaddr.bus,
>>> -                            s->hostaddr.slot, s->hostaddr.function,
>>> -                            errp);
>>> -    if (*errp) {
>>> -        error_append_hint(errp, "Failed to \"open\" the real pci device");
>>> -        return;
>>> -    }
>>> -
>>>      s->is_virtfn = s->real_device.is_virtfn;
>>>      if (s->is_virtfn) {
>>>          XEN_PT_LOG(d, "%04x:%02x:%02x.%d is a SR-IOV Virtual Function\n",
>>> @@ -950,11 +941,50 @@ static void xen_pci_passthrough_instance_init(Object 
>>> *obj)
>>>      PCI_DEVICE(obj)->cap_present |= QEMU_PCI_CAP_EXPRESS;
>>>  }
>>>  
>>> +void xen_igd_reserve_slot(PCIBus *pci_bus)
>>> +{
>>> +    XEN_PT_LOG(0, "Reserving PCI slot 2 for IGD\n");
>>> +    pci_bus->slot_reserved_mask |= XEN_PCI_IGD_SLOT_MASK;
>>> +}
>>> +
>>> +static void xen_igd_clear_slot(DeviceState *qdev, Error **errp)
>>> +{
>>> +    ERRP_GUARD();
>>> +    PCIDevice *pci_dev = (PCIDevice *)qdev;
>>> +    XenPCIPassthroughState *s = XEN_PT_DEVICE(pci_dev);
>>> +    XenPTDeviceClass *xpdc = XEN_PT_DEVICE_GET_CLASS(s);
>>> +    PCIBus *pci_bus = pci_get_bus(pci_dev);
>>> +
>>> +    if (!(pci_bus->slot_reserved_mask & XEN_PCI_IGD_SLOT_MASK))
>>> +        return;
>>> +
>>> +    xen_host_pci_device_get(&s->real_device,
>>> +                            s->hostaddr.domain, s->hostaddr.bus,
>>> +                            s->hostaddr.slot, s->hostaddr.function,
>>> +                            errp);
>>> +    if (*errp) {
>>> +        error_append_hint(errp, "Failed to \"open\" the real pci device");
>>> +        return;
>>> +    }
>>> +
>>> +    if (is_igd_vga_passthrough(&s->real_device) &&
>>> +        s->real_device.domain == 0 && s->real_device.bus == 0 &&
>>> +        s->real_device.dev == 2 && s->real_device.func == 0 &&
>>> +        s->real_device.vendor_id == PCI_VENDOR_ID_INTEL) {
>> 
>> how about macros for these?
>> 
>> #define XEN_PCI_IGD_DOMAIN 0
>> #define XEN_PCI_IGD_BUS 0
>> #define XEN_PCI_IGD_DEV 2
>> #define XEN_PCI_IGD_FN 0
>> 
>>> +        pci_bus->slot_reserved_mask &= ~XEN_PCI_IGD_SLOT_MASK;
>> 
>> If you are going to do this, you should set it back
>> either after pci_qdev_realize or in unrealize,
>> for symmetry.
>> 
>>> +        XEN_PT_LOG(pci_dev, "Intel IGD found, using slot 2\n");
>>> +    }
>> 
>> 
>>> +    xpdc->pci_qdev_realize(qdev, errp);
>>> +}
>>> +
>> 
>> 
>> 
>>>  static void xen_pci_passthrough_class_init(ObjectClass *klass, void *data)
>>>  {
>>>      DeviceClass *dc = DEVICE_CLASS(klass);
>>>      PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
>>>  
>>> +    XenPTDeviceClass *xpdc = XEN_PT_DEVICE_CLASS(klass);
>>> +    xpdc->pci_qdev_realize = dc->realize;
>>> +    dc->realize = xen_igd_clear_slot;
>>>      k->realize = xen_pt_realize;
>>>      k->exit = xen_pt_unregister_device;
>>>      k->config_read = xen_pt_pci_read_config;
>>> @@ -977,6 +1007,7 @@ static const TypeInfo xen_pci_passthrough_info = {
>>>      .instance_size = sizeof(XenPCIPassthroughState),
>>>      .instance_finalize = xen_pci_passthrough_finalize,
>>>      .class_init = xen_pci_passthrough_class_init,
>>> +    .class_size = sizeof(XenPTDeviceClass),
>>>      .instance_init = xen_pci_passthrough_instance_init,
>>>      .interfaces = (InterfaceInfo[]) {
>>>          { INTERFACE_CONVENTIONAL_PCI_DEVICE },
>>> diff --git a/hw/xen/xen_pt.h b/hw/xen/xen_pt.h
>>> index cf10fc7bbf..8c25932b4b 100644
>>> --- a/hw/xen/xen_pt.h
>>> +++ b/hw/xen/xen_pt.h
>>> @@ -2,6 +2,7 @@
>>>  #define XEN_PT_H
>>>  
>>>  #include "hw/xen/xen_common.h"
>>> +#include "hw/pci/pci_bus.h"
>>>  #include "xen-host-pci-device.h"
>>>  #include "qom/object.h"
>>>  
>>> @@ -40,7 +41,20 @@ typedef struct XenPTReg XenPTReg;
>>>  #define TYPE_XEN_PT_DEVICE "xen-pci-passthrough"
>>>  OBJECT_DECLARE_SIMPLE_TYPE(XenPCIPassthroughState, XEN_PT_DEVICE)
>>>  
>>> +#define XEN_PT_DEVICE_CLASS(klass) \
>>> +    OBJECT_CLASS_CHECK(XenPTDeviceClass, klass, TYPE_XEN_PT_DEVICE)
>>> +#define XEN_PT_DEVICE_GET_CLASS(obj) \
>>> +    OBJECT_GET_CLASS(XenPTDeviceClass, obj, TYPE_XEN_PT_DEVICE)
>>> +
>>> +typedef void (*XenPTQdevRealize)(DeviceState *qdev, Error **errp);
>>> +
>>> +typedef struct XenPTDeviceClass {
>>> +    PCIDeviceClass parent_class;
>>> +    XenPTQdevRealize pci_qdev_realize;
>>> +} XenPTDeviceClass;
>>> +
>>>  uint32_t igd_read_opregion(XenPCIPassthroughState *s);
>>> +void xen_igd_reserve_slot(PCIBus *pci_bus);
>>>  void igd_write_opregion(XenPCIPassthroughState *s, uint32_t val);
>>>  void xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
>>>                                             XenHostPCIDevice *dev);
>>> @@ -75,6 +89,8 @@ typedef int (*xen_pt_conf_byte_read)
>>>  
>>>  #define XEN_PCI_INTEL_OPREGION 0xfc
>>>  
>>> +#define XEN_PCI_IGD_SLOT_MASK 0x4UL /* Intel IGD slot_reserved_mask */
>>> +
>> 
>> I think you want to calculate this based on dev fn:
>> 
>> #define XEN_PCI_IGD_SLOT_MASK \
>>      (0x1 << PCI_SLOT(PCI_DEVFN(XEN_PCI_IGD_DEV, XEN_PCI_IGD_FN)))
>> 
>> 
>>>  typedef enum {
>>>      XEN_PT_GRP_TYPE_HARDWIRED = 0,  /* 0 Hardwired reg group */
>>>      XEN_PT_GRP_TYPE_EMU,            /* emul reg group */
>>> diff --git a/hw/xen/xen_pt_stub.c b/hw/xen/xen_pt_stub.c
>>> index 2d8cac8d54..5c108446a8 100644
>>> --- a/hw/xen/xen_pt_stub.c
>>> +++ b/hw/xen/xen_pt_stub.c
>>> @@ -20,3 +20,7 @@ void xen_igd_gfx_pt_set(bool value, Error **errp)
>>>          error_setg(errp, "Xen PCI passthrough support not built in");
>>>      }
>>>  }
>>> +
>>> +void xen_igd_reserve_slot(PCIBus *pci_bus)
>>> +{
>>> +}
>>> -- 
>>> 2.39.0
>> 
>