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

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Date:   Thu, 16 Jul 2020 15:42:52 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH RFC don't apply] vdpa_sim: endian-ness for config space


On 2020/7/16 下午1:42, Michael S. Tsirkin wrote:
> On Wed, Jul 15, 2020 at 10:02:32PM +0800, Jason Wang wrote:
>> On 2020/7/15 下午9:58, 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@...hat.com>
>>
>> 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);