Re: [RFC KERNEL PATCH v2 1/3] xen/pci: Add xen_reset_device_state function

[Chen, Jiqian]

Hi Stewart,

On 2023/11/30 23:03, Stewart Hildebrand wrote:
> On 11/30/23 02:03, Chen, Jiqian wrote:
>>
>> On 2023/11/30 11:46, Stefano Stabellini wrote:
>>> On Fri, 24 Nov 2023, Jiqian Chen wrote:
>>>> When device on dom0 side has been reset, the vpci on Xen side
>>>> won't get notification, so that the cached state in vpci is
>>>> all out of date with the real device state.
>>>> To solve that problem, this patch add a function to clear all
>>>> vpci device state when device is reset on dom0 side.
>>>>
>>>> And call that function in pcistub_init_device. Because when
>>>> we use "pci-assignable-add" to assign a passthrough device in
>>>> Xen, it will reset passthrough device and the vpci state will
>>>> out of date, and then device will fail to restore bar state.
>>>>
>>>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>>>> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
>>>> ---
>>>>  drivers/xen/pci.c                  | 12 ++++++++++++
>>>>  drivers/xen/xen-pciback/pci_stub.c |  3 +++
>>>>  include/xen/interface/physdev.h    |  2 ++
>>>>  include/xen/pci.h                  |  6 ++++++
>>>>  4 files changed, 23 insertions(+)
>>>>
>>>> diff --git a/drivers/xen/pci.c b/drivers/xen/pci.c
>>>> index 72d4e3f193af..e9b30bc09139 100644
>>>> --- a/drivers/xen/pci.c
>>>> +++ b/drivers/xen/pci.c
>>>> @@ -177,6 +177,18 @@ static int xen_remove_device(struct device *dev)
>>>>  	return r;
>>>>  }
>>>>  
>>>> +int xen_reset_device_state(const struct pci_dev *dev)
>>>> +{
>>>> +	struct physdev_pci_device device = {
>>>> +		.seg = pci_domain_nr(dev->bus),
>>>> +		.bus = dev->bus->number,
>>>> +		.devfn = dev->devfn
>>>> +	};
>>>> +
>>>> +	return HYPERVISOR_physdev_op(PHYSDEVOP_pci_device_state_reset, &device);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(xen_reset_device_state);
>>>> +
>>>>  static int xen_pci_notifier(struct notifier_block *nb,
>>>>  			    unsigned long action, void *data)
>>>>  {
>>>> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
>>>> index e34b623e4b41..5a96b6c66c07 100644
>>>> --- a/drivers/xen/xen-pciback/pci_stub.c
>>>> +++ b/drivers/xen/xen-pciback/pci_stub.c
>>>> @@ -421,6 +421,9 @@ static int pcistub_init_device(struct pci_dev *dev)
>>>>  	else {
>>>>  		dev_dbg(&dev->dev, "resetting (FLR, D3, etc) the device\n");
>>>>  		__pci_reset_function_locked(dev);
>>>> +		err = xen_reset_device_state(dev);
>>>> +		if (err)
>>>> +			goto config_release;
>>>
>>> Older versions of Xen won't have the hypercall
>>> PHYSDEVOP_pci_device_state_reset implemented. I think we should do
>>> something like:
>>>
>>> if (err && xen_pvh_domain())
>>>     goto config_release;
>>>
>>>
>>> Or even:
>>>
>>> if (xen_pvh_domain()) {
>>>     err = xen_reset_device_state(dev);
>>>     if (err)
>>>         goto config_release;
>>> }
>>>
>>> depending on whether we want to call xen_reset_device_state also for PV
>>> guests or not. I am assuming we don't want to error out on failure such
>>> as -ENOENT for PV guests.
>> Yes, only for PVH dom0, I will add the condition in next version. Thank you!
> 
> We will want to call xen_reset_device_state() for Arm dom0, too, so checking xen_pvh_domain() alone is not sufficient. I suggest instead to check !xen_pv_domain().
I am not using Arm. But is Arm dom0 not a PVH type dom0?

> 
>>
>>>
>>>
>>>>  		pci_restore_state(dev);
>>>>  	}
>>>>  	/* Now disable the device (this also ensures some private device
>>>> diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
>>>> index a237af867873..231526f80f6c 100644
>>>> --- a/include/xen/interface/physdev.h
>>>> +++ b/include/xen/interface/physdev.h
>>>> @@ -263,6 +263,8 @@ struct physdev_pci_device {
>>>>      uint8_t devfn;
>>>>  };
>>>>  
>>>> +#define PHYSDEVOP_pci_device_state_reset     32
>>>> +
>>>>  #define PHYSDEVOP_DBGP_RESET_PREPARE    1
>>>>  #define PHYSDEVOP_DBGP_RESET_DONE       2
>>>>  
>>>> diff --git a/include/xen/pci.h b/include/xen/pci.h
>>>> index b8337cf85fd1..b2e2e856efd6 100644
>>>> --- a/include/xen/pci.h
>>>> +++ b/include/xen/pci.h
>>>> @@ -4,10 +4,16 @@
>>>>  #define __XEN_PCI_H__
>>>>  
>>>>  #if defined(CONFIG_XEN_DOM0)
>>>> +int xen_reset_device_state(const struct pci_dev *dev);
>>>>  int xen_find_device_domain_owner(struct pci_dev *dev);
>>>>  int xen_register_device_domain_owner(struct pci_dev *dev, uint16_t domain);
>>>>  int xen_unregister_device_domain_owner(struct pci_dev *dev);
>>>>  #else
>>>> +static inline int xen_reset_device_state(const struct pci_dev *dev)
>>>> +{
>>>> +	return -1;
>>>> +}
>>>> +
>>>>  static inline int xen_find_device_domain_owner(struct pci_dev *dev)
>>>>  {
>>>>  	return -1;
>>>> -- 
>>>> 2.34.1
>>>>
>>

-- 
Best regards,
Jiqian Chen.