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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>
Cc:     linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <0ad1b5e6-52a8-aa4c-ec5f-a44a5727d84d@redhat.com>
Date:   Thu, 6 Aug 2020 11:23:45 +0800
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On 2020/8/5 下午8:06, Michael S. Tsirkin wrote:
> On Wed, Aug 05, 2020 at 02:21:07PM +0800, Jason Wang wrote:
>> 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
> So how about I add a comment along the lines of
>
> /*
>   * vdpasim ATM requires VIRTIO_F_ACCESS_PLATFORM, so we don't need to
>   * support legacy guests. Keep transitional device code around for
>   * the benefit of people who might copy-and-paste this into transitional
>   * device code.
>   */


That's fine.

Thanks


>
>