linux-kernel - Re: [PATCH] vdpa_sim: do not reset IOTLB during device reset

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Date:   Thu, 14 May 2020 05:35:27 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vdpa_sim: do not reset IOTLB during device reset

On Thu, May 14, 2020 at 03:25:49PM +0800, Jason Wang wrote:
> We reset IOTLB during device reset this breaks the assumption that the
> mapping needs to be controlled via vDPA DMA ops explicitly in a
> incremental way. So the networking will be broken after e.g a guest
> reset.
> 
> Fix this by not resetting the IOTLB during device reset.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>


That's a bit weird, and can be a security risk if state
leaks between security domains through this.
And there's 0 chance any hardware implementation can
keep the translations around across resets - there
is simply nowhere to keep them.

IMHO we need a different way to make this work, simulator
needs to look like a hardware device as much as possible.


> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 7957d2d41fc4..cc5525743a25 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -119,8 +119,6 @@ static void vdpasim_reset(struct vdpasim *vdpasim)
>  	for (i = 0; i < VDPASIM_VQ_NUM; i++)
>  		vdpasim_vq_reset(&vdpasim->vqs[i]);
>  
> -	vhost_iotlb_reset(vdpasim->iommu);
> -
>  	vdpasim->features = 0;
>  	vdpasim->status = 0;
>  	++vdpasim->generation;
> -- 
> 2.20.1