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

[Chuck Zmudzinski <brchuckz@xxxxxxx>]

On 1/12/23 2:18 PM, Bernhard Beschow wrote:
> 
> 
> 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 the old and no longer maintained Qemu traditional device model available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 think what you are saying is that if I try to move the logic of my patch to 
xen-hvm.c, as Michael suggests, I should not move or copy any piix3 code to the 
Xen integration code, but access it via an appropriate qom interface to the 
code in pc_piix.c and only move Xen specific things to the Xen integration code 
such as the content of my patch. I can try to do that for a v9 of my patch. It 
might take me a little while (I am not a professional coder), so I will just 
leave v8 of my patch as is for now until I have a patch ready to move it out of 
pc_piix.c the qom way.

Thanks,

Chuck

> 
> 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
>>> 
>>