Re: [PATCH RFC don't apply] vdpa_sim: endian-ness for config space

[Jason Wang]

On 2020/7/16 äå1:42, Michael S. Tsirkin wrote:
> On Wed, Jul 15, 2020 at 10:02:32PM +0800, Jason Wang wrote:
> > On 2020/7/15 äå9:58, Michael S. Tsirkin wrote:
> > > VDPA sim stores config space as native endian, but that
> > > is wrong: modern guests expect LE.
> > > I coded up the following to fix it up, but it is wrong too:
> > > vdpasim_create is called before guest features are known.
> > >
> > > So what should we do? New ioctl to specify the interface used?
> > > More ideas?
> > >
> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> >
> > Can we do the endian conversion in set_config/get_config()?
> >
> > Thanks
> That is problematic at least from static checking point of view.


I don't get here. I thought it's just leXX_to_cpu() conversion in 
set_config()/get_config() as what is done in MMIO's vm_set/vm_get.


> It would be reasonable to do it in vdpasim_set_features, except
> legacy guests might not set features at all.
> So my proposal is:
> - set config in vdpasim_set_features


Just to make sure I understand here. What's the meaning of "set config" 
do you mean setup the config space? If yes, and if there's a device 
config space, we still need to do the endian conversion?


> - document that this is where devices should initialize config
> - vdpa core will maintain a "features set" flag, if get/set config
>    is called without set features, core will call set features
>    automatically with 0 value.


Ok, I think you meant checking FEATURE_OK via get_status in vDPA core?

Thanks



> Thoughts?
>
>
> > > ---
> > >    drivers/vdpa/vdpa_sim/vdpa_sim.c | 22 ++++++++++++++++++++--
> > >    1 file changed, 20 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > index a9bc5e0fb353..cc754ae0ec15 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)
> > > @@ -332,8 +350,8 @@ static struct vdpasim *vdpasim_create(void)
> > >    		goto err_iommu;
> > >    	config = &vdpasim->config;
> > > -	config->mtu = 1500;
> > > -	config->status = VIRTIO_NET_S_LINK_UP;
> > > +	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> > > +	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
> > >    	eth_random_addr(config->mac);
> > >    	vringh_set_iotlb(&vdpasim->vqs[0].vring, vdpasim->iommu);