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Date:   Wed, 4 Jan 2023 01:50:03 -0500
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     "Longpeng(Mike)" <longpeng2@huawei.com>
Cc:     jasowang@redhat.com, sgarzare@redhat.com, arei.gonglei@huawei.com,
        yechuan@huawei.com, huangzhichao@huawei.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] vp_vdpa: harden the logic of set status
Message-ID: <20230104014642-mutt-send-email-mst@kernel.org>
References: <20230104042519.170-1-longpeng2@huawei.com>
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On Wed, Jan 04, 2023 at 12:25:19PM +0800, Longpeng(Mike) wrote:
> From: Longpeng <longpeng2@huawei.com>
> 
> 1. We should not set status to 0 when invoking vp_vdpa_set_status(),
>    trigger a warning in that case.
> 
> 2. The driver MUST wait for a read of device_status to return 0 before
>    reinitializing the device. But we also don't want to keep us in an
>    infinite loop forever, so wait for 5s if we try to reset the device.
> 
> Signed-off-by: Longpeng <longpeng2@huawei.com>
> ---
> Changes v3->v2:
>  - move VP_VDPA_RESET_TIMEOUT_US near the other macros. [Stefano]
>  - refer v1.2 in comments. [Stefano]
>  - s/keep/keeping/  [Jason]
>  - use readx_poll_timeout. [Jason]
> 
> Changes v1->v2:
>  - use WARN_ON instead of BUG_ON. [Stefano]
>  - use "warning + failed" instead of "infinite loop". [Jason, Stefano]
>  - use usleep_range instead of msleep (checkpatch). [Longpeng]
> 
> ---
>  drivers/vdpa/virtio_pci/vp_vdpa.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> index d448db0c4de3..3fc496aea456 100644
> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> @@ -10,6 +10,7 @@
>  
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
> +#include <linux/iopoll.h>
>  #include <linux/pci.h>
>  #include <linux/vdpa.h>
>  #include <linux/virtio.h>
> @@ -22,6 +23,7 @@
>  #define VP_VDPA_QUEUE_MAX 256
>  #define VP_VDPA_DRIVER_NAME "vp_vdpa"
>  #define VP_VDPA_NAME_SIZE 256
> +#define VP_VDPA_RESET_TIMEOUT_US 5000000 /* 5s */
>  
>  struct vp_vring {
>  	void __iomem *notify;
> @@ -214,6 +216,9 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
>  	struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
>  	u8 s = vp_vdpa_get_status(vdpa);
>  
> +	/* We should never be setting status to 0. */
> +	WARN_ON(status == 0);
> +
>  	if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
>  	    !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
>  		vp_vdpa_request_irq(vp_vdpa);

Isn't this user-triggerable? What prevents that?

> @@ -226,10 +231,25 @@ static int vp_vdpa_reset(struct vdpa_device *vdpa)
>  {
>  	struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
>  	struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
> -	u8 s = vp_vdpa_get_status(vdpa);
> +	u8 tmp, s = vp_vdpa_get_status(vdpa);
> +	int ret;
>  
>  	vp_modern_set_status(mdev, 0);
>  
> +	/*
> +	 * As the virtio v1.1/v1.2 spec (4.1.4.3.2) says: After writing 0 to
> +	 * device_status, the driver MUST wait for a read of device_status
> +	 * to return 0 before reinitializing the device.
> +	 * To avoid keeping us here forever, we only wait for 5 seconds.
> +	 */
> +	ret = readx_poll_timeout(vp_ioread8, &mdev->common->device_status, tmp,
> +				 tmp == 0, 1000, VP_VDPA_RESET_TIMEOUT_US);
> +	if (ret) {
> +		dev_err(&mdev->pci_dev->dev,
> +			"vp_vdpa: fail to reset device, %d\n", ret);
> +		return ret;
> +	}
> +
>  	if (s & VIRTIO_CONFIG_S_DRIVER_OK)
>  		vp_vdpa_free_irq(vp_vdpa);

Do all callers actually check return status of reset?
If not they will happily reinitialize the device and violate the spec.


> -- 
> 2.23.0