Re: [RFC KERNEL PATCH v3 1/3] xen/pci: Add xen_reset_device_state function

["Roger Pau Monné" <roger.pau@citrix.com>]

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 all out of date with the real device state.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 out of date, and then device will fail to restore bar state.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

Overall I'm not sure why the hypercall wrapper needs to live in
xen/pci.c.  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.

Thanks, Roger.