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

[Bernhard Beschow <shentey@xxxxxxxxx>]

Am 12. Januar 2023 20:11:54 UTC schrieb 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 the old and no longer maintained Qemu traditional device model available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.

I think the change Michael suggests is very minimalistic: Move the if condition 
around xen_igd_reserve_slot() into the function itself and always call it there 
unconditionally -- basically turning three lines into one. Since 
xen_igd_reserve_slot() seems very problem specific, Michael further suggests to 
rename it to something more general. All in all no big changes required.

Best regards,
Bernhard

>
>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
>>>> 
>>>
>