linux-kernel - Re: [PATCH v2] vfio/pci: Support error recovery

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Date:   Tue, 10 Jan 2017 01:04:06 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Cao jin <caoj.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        qemu-devel@...gnu.org, izumi.taku@...fujitsu.com,
        alex.williamson@...hat.com
Subject: Re: [PATCH v2] vfio/pci: Support error recovery

On Sat, Dec 31, 2016 at 05:15:36PM +0800, Cao jin wrote:
> Support serious device error recovery

serious?

> 
> Signed-off-by: Cao jin <caoj.fnst@...fujitsu.com>
> ---
>  drivers/vfio/pci/vfio_pci.c         | 70 +++++++++++++++++++++++++++++++++++--
>  drivers/vfio/pci/vfio_pci_private.h |  2 ++
>  2 files changed, 70 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 712a849..752af20 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -534,6 +534,15 @@ static long vfio_pci_ioctl(void *device_data,
>  {
>  	struct vfio_pci_device *vdev = device_data;
>  	unsigned long minsz;
> +	int ret;
> +
> +	if (vdev->aer_recovering && (cmd == VFIO_DEVICE_SET_IRQS ||
> +	    cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
> +		ret = wait_for_completion_interruptible(
> +			&vdev->aer_completion);

don't split it like that.

> +		if (ret)
> +			return ret;
> +	}
>  
>  	if (cmd == VFIO_DEVICE_GET_INFO) {
>  		struct vfio_device_info info;
> @@ -953,6 +962,15 @@ static ssize_t vfio_pci_rw(void *device_data, char __user *buf,
>  {
>  	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
>  	struct vfio_pci_device *vdev = device_data;
> +	int ret;
> +
> +	/* block all kinds of access during host recovery */
> +	if (vdev->aer_recovering) {
> +		ret = wait_for_completion_interruptible(
> +			&vdev->aer_completion);
> +		if (ret)
> +			return ret;
> +	}
>  
>  	if (index >= VFIO_PCI_NUM_REGIONS + vdev->num_regions)
>  		return -EINVAL;
> @@ -1117,6 +1135,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	vdev->irq_type = VFIO_PCI_NUM_IRQS;
>  	mutex_init(&vdev->igate);
>  	spin_lock_init(&vdev->irqlock);
> +	init_completion(&vdev->aer_completion);
>  
>  	ret = vfio_add_group_dev(&pdev->dev, &vfio_pci_ops, vdev);
>  	if (ret) {
> @@ -1176,6 +1195,9 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>  {
>  	struct vfio_pci_device *vdev;
>  	struct vfio_device *device;
> +	u32 uncor_status;
> +	unsigned int aer_cap_offset;
> +	int ret;
>  
>  	device = vfio_device_get_from_dev(&pdev->dev);
>  	if (device == NULL)
> @@ -1187,10 +1209,29 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>  		return PCI_ERS_RESULT_DISCONNECT;
>  	}
>  
> +	/*
> +	 * get device's uncorrectable error status as soon as possible,

should be "Get".

> +	 * and signal it to user space. The later we read it, the possibility
> +	 * the register value is mangled grows.
> +	 */
> +	aer_cap_offset = pci_find_ext_capability(vdev->pdev, PCI_EXT_CAP_ID_ERR);
> +	ret = pci_read_config_dword(vdev->pdev, aer_cap_offset +
> +                                    PCI_ERR_UNCOR_STATUS, &uncor_status);
> +        if (ret)
> +                return PCI_ERS_RESULT_DISCONNECT;
> +
> +	pr_info("device %d got AER detect notification. uncorrectable error status = 0x%x\n", pdev->devfn, uncor_status);//to be removed

Pls drop this.

>  	mutex_lock(&vdev->igate);
>  
> -	if (vdev->err_trigger)
> -		eventfd_signal(vdev->err_trigger, 1);
> +	vdev->aer_recovering = true;
> +	reinit_completion(&vdev->aer_completion);
> +
> +	if (vdev->err_trigger && uncor_status) {
> +		pr_info("device %d signal uncor status 0x%x to user",
> +			pdev->devfn, uncor_status);
> +		/* signal uncorrectable error status to user space */
> +		eventfd_signal(vdev->err_trigger, uncor_status);
> +        }
>  
>  	mutex_unlock(&vdev->igate);
>  
> @@ -1199,8 +1240,33 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>  	return PCI_ERS_RESULT_CAN_RECOVER;
>  }
>  
> +static void vfio_pci_aer_resume(struct pci_dev *pdev)
> +{
> +	struct vfio_pci_device *vdev;
> +	struct vfio_device *device;
> +
> +	device = vfio_device_get_from_dev(&pdev->dev);
> +	if (device == NULL)
> +		return;
> +
> +	vdev = vfio_device_data(device);
> +	if (vdev == NULL) {
> +		vfio_device_put(device);
> +		return;
> +	}
> +
> +	mutex_lock(&vdev->igate);
> +	vdev->aer_recovering = false;
> +	mutex_unlock(&vdev->igate);
> +
> +	complete_all(&vdev->aer_completion);
> +
> +	vfio_device_put(device);
> +}
> +
>  static const struct pci_error_handlers vfio_err_handlers = {
>  	.error_detected = vfio_pci_aer_err_detected,
> +	.resume         = vfio_pci_aer_resume,
>  };
>  
>  static struct pci_driver vfio_pci_driver = {
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 8a7d546..ba8471f 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -83,6 +83,8 @@ struct vfio_pci_device {
>  	bool			bardirty;
>  	bool			has_vga;
>  	bool			needs_reset;
> +	bool			aer_recovering;
> +	struct completion	aer_completion;
>  	struct pci_saved_state	*pci_saved_state;
>  	int			refcnt;
>  	struct eventfd_ctx	*err_trigger;
> -- 
> 1.8.3.1
> 
> 

How about some explanation about what is going on here?  All these
changes seem racy since any number of errors can trigger at any time.

-- 
MST