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

[Stewart Hildebrand <stewart.hildebrand@amd.com>]

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 all out of date with the real device state.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 out of date, and then device will fail to restore bar state.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@amd.com>
>>> Signed-off-by: Huang Rui <ray.huang@amd.com>
>>> ---
>>>  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().

> 
>>
>>
>>>  		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
>>>
>