linux-kernel - Re: [PATCH V2 5/5] vdpa: mlx5: support per virtqueue dma device

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Date:   Fri, 3 Feb 2023 04:33:21 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     elic@...dia.com, gdawar@....com, tanuj.kamde@....com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH V2 5/5] vdpa: mlx5: support per virtqueue dma device

On Thu, Jan 19, 2023 at 02:15:25PM +0800, Jason Wang wrote:
> This patch implements per virtqueue dma device for mlx5_vdpa. This is
> needed for virtio_vdpa to work for CVQ which is backed by vringh but
> not DMA. We simply advertise the vDPA device itself as the DMA device
> for CVQ then DMA API can simply use PA so the identical mapping for
> CVQ can still be used. Otherwise the identical (1:1) mapping won't
> work when platform IOMMU is enabled since the IOVA is allocated on
> demand which is not necessarily the PA.
> 
> This fixes the following crash when mlx5 vDPA device is bound to
> virtio-vdpa with platform IOMMU enabled but not in passthrough mode:
> 
> BUG: unable to handle page fault for address: ff2fb3063deb1002
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 1393001067 P4D 1393002067 PUD 0
> Oops: 0000 [#1] PREEMPT SMP NOPTI
> CPU: 55 PID: 8923 Comm: kworker/u112:3 Kdump: loaded Not tainted 6.1.0+ #7
> Hardware name: Dell Inc. PowerEdge R750/0PJ80M, BIOS 1.5.4 12/17/2021
> Workqueue: mlx5_vdpa_wq mlx5_cvq_kick_handler [mlx5_vdpa]
> RIP: 0010:vringh_getdesc_iotlb+0x93/0x1d0 [vringh]
> Code: 14 25 40 ef 01 00 83 82 c0 0a 00 00 01 48 2b 05 93 5a 1b ea 8b 4c 24 14 48 c1 f8 06 48 c1 e0 0c 48 03 05 90 5a 1b ea 48 01 c8 <0f> b7 00 83 aa c0 0a 00 00 01 65 ff 0d bc e4 41 3f 0f 84 05 01 00
> RSP: 0018:ff46821ba664fdf8 EFLAGS: 00010282
> RAX: ff2fb3063deb1002 RBX: 0000000000000a20 RCX: 0000000000000002
> RDX: ff2fb318d2f94380 RSI: 0000000000000002 RDI: 0000000000000001
> RBP: ff2fb3065e832410 R08: ff46821ba664fe00 R09: 0000000000000001
> R10: 0000000000000000 R11: 000000000000000d R12: ff2fb3065e832488
> R13: ff2fb3065e8324a8 R14: ff2fb3065e8324c8 R15: ff2fb3065e8324a8
> FS:  0000000000000000(0000) GS:ff2fb3257fac0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ff2fb3063deb1002 CR3: 0000001392010006 CR4: 0000000000771ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
> <TASK>
>   mlx5_cvq_kick_handler+0x89/0x2b0 [mlx5_vdpa]
>   process_one_work+0x1e2/0x3b0
>   ? rescuer_thread+0x390/0x390
>   worker_thread+0x50/0x3a0
>   ? rescuer_thread+0x390/0x390
>   kthread+0xd6/0x100
>   ? kthread_complete_and_exit+0x20/0x20
>   ret_from_fork+0x1f/0x30
>   </TASK>
> 
> Reviewed-by: Eli Cohen <elic@...dia.com>
> Tested-by: Eli Cohen <elic@...dia.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Jason how about a Fixes tag here?

> ---
> Changes since V1:
> - make mlx5_get_vq_dma_dev() static
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 6632651b1e54..97d1ada7f4db 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -2682,6 +2682,16 @@ static int mlx5_vdpa_set_map(struct vdpa_device *vdev, unsigned int asid,
>  	return err;
>  }
>  
> +static struct device *mlx5_get_vq_dma_dev(struct vdpa_device *vdev, u16 idx)
> +{
> +	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> +
> +	if (is_ctrl_vq_idx(mvdev, idx))
> +		return &vdev->dev;
> +
> +	return mvdev->vdev.dma_dev;
> +}
> +
>  static void mlx5_vdpa_free(struct vdpa_device *vdev)
>  {
>  	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> @@ -2897,6 +2907,7 @@ static const struct vdpa_config_ops mlx5_vdpa_ops = {
>  	.get_generation = mlx5_vdpa_get_generation,
>  	.set_map = mlx5_vdpa_set_map,
>  	.set_group_asid = mlx5_set_group_asid,
> +	.get_vq_dma_dev = mlx5_get_vq_dma_dev,
>  	.free = mlx5_vdpa_free,
>  	.suspend = mlx5_vdpa_suspend,
>  };
> -- 
> 2.25.1