Re: [PATCH v4 1/6] vfio/pci: Mask INTx during runtime suspend

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 1 Jul 2022 16:38:09 +0530
Abhishek Sahu <abhsahu@nvidia.com> wrote:

> This patch adds INTx handling during runtime suspend/resume.
> All the suspend/resume related code for the user to put the device
> into the low power state will be added in subsequent patches.
> 
> The INTx are shared among devices. Whenever any INTx interrupt comes

"The INTx lines may be shared..."

> for the VFIO devices, then vfio_intx_handler() will be called for each
> device. Inside vfio_intx_handler(), it calls pci_check_and_mask_intx()

"...device sharing the interrupt."

> and checks if the interrupt has been generated for the current device.
> Now, if the device is already in the D3cold state, then the config space
> can not be read. Attempt to read config space in D3cold state can
> cause system unresponsiveness in a few systems. To prevent this, mask
> INTx in runtime suspend callback and unmask the same in runtime resume
> callback. If INTx has been already masked, then no handling is needed
> in runtime suspend/resume callbacks. 'pm_intx_masked' tracks this, and
> vfio_pci_intx_mask() has been updated to return true if INTx has been
> masked inside this function.
> 
> For the runtime suspend which is triggered for the no user of VFIO
> device, the is_intx() will return false and these callbacks won't do
> anything.
> 
> The MSI/MSI-X are not shared so similar handling should not be
> needed for MSI/MSI-X. vfio_msihandler() triggers eventfd_signal()
> without doing any device-specific config access. When the user performs
> any config access or IOCTL after receiving the eventfd notification,
> then the device will be moved to the D0 state first before
> servicing any request.
> 
> Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c  | 37 +++++++++++++++++++++++++++----
>  drivers/vfio/pci/vfio_pci_intrs.c |  6 ++++-
>  include/linux/vfio_pci_core.h     |  3 ++-
>  3 files changed, 40 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index a0d69ddaf90d..5948d930449b 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -259,16 +259,45 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat
>  	return ret;
>  }
>  
> +#ifdef CONFIG_PM
> +static int vfio_pci_core_runtime_suspend(struct device *dev)
> +{
> +	struct vfio_pci_core_device *vdev = dev_get_drvdata(dev);
> +
> +	/*
> +	 * If INTx is enabled, then mask INTx before going into the runtime
> +	 * suspended state and unmask the same in the runtime resume.
> +	 * If INTx has already been masked by the user, then
> +	 * vfio_pci_intx_mask() will return false and in that case, INTx
> +	 * should not be unmasked in the runtime resume.
> +	 */
> +	vdev->pm_intx_masked = (is_intx(vdev) && vfio_pci_intx_mask(vdev));
> +
> +	return 0;
> +}
> +
> +static int vfio_pci_core_runtime_resume(struct device *dev)
> +{
> +	struct vfio_pci_core_device *vdev = dev_get_drvdata(dev);
> +
> +	if (vdev->pm_intx_masked)
> +		vfio_pci_intx_unmask(vdev);
> +
> +	return 0;
> +}
> +#endif /* CONFIG_PM */
> +
>  /*
> - * The dev_pm_ops needs to be provided to make pci-driver runtime PM working,
> - * so use structure without any callbacks.
> - *
>   * The pci-driver core runtime PM routines always save the device state
>   * before going into suspended state. If the device is going into low power
>   * state with only with runtime PM ops, then no explicit handling is needed
>   * for the devices which have NoSoftRst-.
>   */
> -static const struct dev_pm_ops vfio_pci_core_pm_ops = { };
> +static const struct dev_pm_ops vfio_pci_core_pm_ops = {
> +	SET_RUNTIME_PM_OPS(vfio_pci_core_runtime_suspend,
> +			   vfio_pci_core_runtime_resume,
> +			   NULL)
> +};
>  
>  int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
>  {
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 6069a11fb51a..1a37db99df48 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -33,10 +33,12 @@ static void vfio_send_intx_eventfd(void *opaque, void *unused)
>  		eventfd_signal(vdev->ctx[0].trigger, 1);
>  }
>  
> -void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
> +/* Returns true if INTx has been masked by this function. */
> +bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
>  {
>  	struct pci_dev *pdev = vdev->pdev;
>  	unsigned long flags;
> +	bool intx_masked = false;
>  
>  	spin_lock_irqsave(&vdev->irqlock, flags);
>  
> @@ -60,9 +62,11 @@ void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
>  			disable_irq_nosync(pdev->irq);
>  
>  		vdev->ctx[0].masked = true;
> +		intx_masked = true;
>  	}
>  
>  	spin_unlock_irqrestore(&vdev->irqlock, flags);
> +	return intx_masked;
>  }


There's certainly another path through this function that masks the
interrupt, which makes the definition of this return value a bit
confusing.  Wouldn't it be simpler not to overload the masked flag on
the interrupt context like this and instead set a new flag on the vdev
under irqlock to indicate the device is unable to generate interrupts.
The irq handler would add a test of this flag before any tests that
would access the device.  Thanks,

Alex
 
>  /*
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index 23c176d4b073..cdfd328ba6b1 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -124,6 +124,7 @@ struct vfio_pci_core_device {
>  	bool			needs_reset;
>  	bool			nointx;
>  	bool			needs_pm_restore;
> +	bool			pm_intx_masked;
>  	struct pci_saved_state	*pci_saved_state;
>  	struct pci_saved_state	*pm_save;
>  	int			ioeventfds_nr;
> @@ -147,7 +148,7 @@ struct vfio_pci_core_device {
>  #define is_irq_none(vdev) (!(is_intx(vdev) || is_msi(vdev) || is_msix(vdev)))
>  #define irq_is(vdev, type) (vdev->irq_type == type)
>  
> -extern void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
> +extern bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
>  extern void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);
>  
>  extern int vfio_pci_set_irqs_ioctl(struct vfio_pci_core_device *vdev,