linux-kernel - Re: [RFC KERNEL PATCH v3 1/3] xen/pci: Add xen_reset_device

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Date:   Wed, 13 Dec 2023 03:02:08 +0000
From:   "Chen, Jiqian" <Jiqian.Chen@....com>
To:     Roger Pau Monné <roger.pau@...rix.com>
CC:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "Hildebrand, Stewart" <Stewart.Hildebrand@....com>,
        "Huang, Ray" <Ray.Huang@....com>,
        "Chen, Jiqian" <Jiqian.Chen@....com>
Subject: Re: [RFC KERNEL PATCH v3 1/3] xen/pci: Add xen_reset_device_state
 function

On 2023/12/12 16:08, Roger Pau Monné wrote:
> On Mon, Dec 11, 2023 at 12:15:17AM +0800, 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 all out of date with the real device state.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, add a new function to clear all vpci
>> device state when device is reset on dom0 side.
>>
>> And call that function in pcistub_init_device. Because when
>> using "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 out of date, and then device will fail to restore bar state.
>>
>> Co-developed-by: Huang Rui <ray.huang@....com>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@....com>
>> ---
>>  drivers/xen/pci.c                  | 12 ++++++++++++
>>  drivers/xen/xen-pciback/pci_stub.c |  4 ++++
>>  include/xen/interface/physdev.h    |  8 ++++++++
>>  include/xen/pci.h                  |  6 ++++++
>>  4 files changed, 30 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..24f599eaec14 100644
>> --- a/drivers/xen/xen-pciback/pci_stub.c
>> +++ b/drivers/xen/xen-pciback/pci_stub.c
>> @@ -421,6 +421,10 @@ 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);
>> +		if (!xen_pv_domain())
>> +			err = xen_reset_device_state(dev);
>> +		if (err)
>> +			goto config_release;
> 
> I think you are missing other instances where
> __pci_reset_function_locked() is called in pci_stub.c?  See
> pcistub_device_release() and pcistub_put_pci_dev().
Sorry, I didn't consider the situation to free passthrough device. You are right.

> 
> Overall I'm not sure why the hypercall wrapper needs to live in
> xen/pci.c.  
For other possible scenarios where this function may be used?

> I think it would be better if you could create a static wrapper in pci_stub.c that does the call to
> __pci_reset_function_locked() plus PHYSDEVOP_pci_device_state_reset.
> That would make it less likely that new callers of
> __pci_reset_function_locked() are introduced without noticing the need
> to also call PHYSDEVOP_pci_device_state_reset.
Ok, I will add a new function to do __pci_reset_function_locked and PHYSDEVOP_pci_device_state_reset in pci_stub.c

> 
> Thanks, Roger.

-- 
Best regards,
Jiqian Chen.