linux-kernel - Re: [PATCH] xen: introduce xen_vring_use

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Date:   Wed, 24 Jun 2020 05:06:48 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Peng Fan <peng.fan@....com>
Cc:     sstabellini@...nel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, konrad.wilk@...cle.com, jasowang@...hat.com,
        x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        virtualization@...ts.linux-foundation.org, linux-imx@....com
Subject: Re: [PATCH] xen: introduce xen_vring_use_dma

On Wed, Jun 24, 2020 at 05:17:32PM +0800, Peng Fan wrote:
> Export xen_swiotlb for all platforms using xen swiotlb
> 
> Use xen_swiotlb to determine when vring should use dma APIs to map the
> ring: when xen_swiotlb is enabled the dma API is required. When it is
> disabled, it is not required.
> 
> Signed-off-by: Peng Fan <peng.fan@....com>

Isn't there some way to use VIRTIO_F_IOMMU_PLATFORM for this?
Xen was there first, but everyone else is using that now.


> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a2de775801af..768afd79f67a 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -252,7 +252,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
>  	 * the DMA API if we're a Xen guest, which at least allows
>  	 * all of the sensible Xen configurations to work correctly.
>  	 */
> -	if (xen_domain())
> +	if (xen_vring_use_dma())
>  		return true;
>  
>  	return false;


The comment above this should probably be fixed.

-- 
MST