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Subject: Re: [PATCH v2 22/24] vdpa_sim: fix endian-ness of config space
To:     "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org
Cc:     virtualization@lists.linux-foundation.org
References: <20200803205814.540410-1-mst@redhat.com>
 <20200803205814.540410-23-mst@redhat.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <dd24f2e6-4aef-4a26-374c-2349fe1e6a66@redhat.com>
Date:   Wed, 5 Aug 2020 14:21:07 +0800
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On 2020/8/4 上午5:00, Michael S. Tsirkin wrote:
> VDPA sim accesses config space as native endian - this is
> wrong since it's a modern device and actually uses LE.
>
> It only supports modern guests so we could punt and
> just force LE, but let's use the full virtio APIs since people
> tend to copy/paste code, and this is not data path anyway.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>   drivers/vdpa/vdpa_sim/vdpa_sim.c | 31 ++++++++++++++++++++++++++-----
>   1 file changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index a9bc5e0fb353..fa05e065ff69 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -24,6 +24,7 @@
>   #include <linux/etherdevice.h>
>   #include <linux/vringh.h>
>   #include <linux/vdpa.h>
> +#include <linux/virtio_byteorder.h>
>   #include <linux/vhost_iotlb.h>
>   #include <uapi/linux/virtio_config.h>
>   #include <uapi/linux/virtio_net.h>
> @@ -72,6 +73,23 @@ struct vdpasim {
>   	u64 features;
>   };
>   
> +/* TODO: cross-endian support */
> +static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
> +{
> +	return virtio_legacy_is_little_endian() ||
> +		(vdpasim->features & (1ULL << VIRTIO_F_VERSION_1));
> +}
> +
> +static inline u16 vdpasim16_to_cpu(struct vdpasim *vdpasim, __virtio16 val)
> +{
> +	return __virtio16_to_cpu(vdpasim_is_little_endian(vdpasim), val);
> +}
> +
> +static inline __virtio16 cpu_to_vdpasim16(struct vdpasim *vdpasim, u16 val)
> +{
> +	return __cpu_to_virtio16(vdpasim_is_little_endian(vdpasim), val);
> +}
> +
>   static struct vdpasim *vdpasim_dev;
>   
>   static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
> @@ -306,7 +324,6 @@ static const struct vdpa_config_ops vdpasim_net_config_ops;
>   
>   static struct vdpasim *vdpasim_create(void)
>   {
> -	struct virtio_net_config *config;
>   	struct vdpasim *vdpasim;
>   	struct device *dev;
>   	int ret = -ENOMEM;
> @@ -331,10 +348,7 @@ static struct vdpasim *vdpasim_create(void)
>   	if (!vdpasim->buffer)
>   		goto err_iommu;
>   
> -	config = &vdpasim->config;
> -	config->mtu = 1500;
> -	config->status = VIRTIO_NET_S_LINK_UP;
> -	eth_random_addr(config->mac);
> +	eth_random_addr(vdpasim->config.mac);
>   
>   	vringh_set_iotlb(&vdpasim->vqs[0].vring, vdpasim->iommu);
>   	vringh_set_iotlb(&vdpasim->vqs[1].vring, vdpasim->iommu);
> @@ -448,6 +462,7 @@ static u64 vdpasim_get_features(struct vdpa_device *vdpa)
>   static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
>   {
>   	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +	struct virtio_net_config *config = &vdpasim->config;
>   
>   	/* DMA mapping must be done by driver */
>   	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
> @@ -455,6 +470,12 @@ static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
>   
>   	vdpasim->features = features & vdpasim_features;
>   
> +	/* We only know whether guest is using the legacy interface here, so
> +	 * that's the earliest we can set config fields.
> +	 */


We check whether or not ACCESS_PLATFORM is set before which is probably 
a hint that only modern device is supported. So I wonder just force LE 
and fail if VERSION_1 is not set is better?

Thanks


> +
> +	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> +	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
>   	return 0;
>   }
>