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

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

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 all out of date with the real device state.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 out of date, and then device will fail to restore bar state.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!

> 
> 
>>              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.