? 2021/4/25 ??9:25, Eli Cohen ??:> On Thu, Apr 22, 2021 at 04:59:11PM +0800, Jason Wang wrote:
>> ? 2021/4/22 ??4:39, Eli Cohen ??:
>>> On Thu, Apr 22, 2021 at 04:21:45PM +0800, Jason Wang wrote:
>>>> ? 2021/4/22 ??4:07, Eli Cohen ??:
>>>>> On Thu, Apr 22, 2021 at 09:03:58AM +0300, Eli Cohen wrote:
>>>>>> On Thu, Apr 22, 2021 at 10:37:38AM +0800, Jason Wang
wrote:
>>>>>>> ? 2021/4/21 ??6:41, Eli Cohen ??:
>>>>>>>> Implement mlx5_get_vq_notification() to return
the doorbell address.
>>>>>>>> Size is set to one system page as required.
>>>>>>>>
>>>>>>>> Signed-off-by: Eli Cohen <elic at
nvidia.com>
>>>>>>>> ---
>>>>>>>> drivers/vdpa/mlx5/core/mlx5_vdpa.h | 1 +
>>>>>>>> drivers/vdpa/mlx5/core/resources.c | 1 +
>>>>>>>> drivers/vdpa/mlx5/net/mlx5_vnet.c | 6
++++++
>>>>>>>> 3 files changed, 8 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>>>>>> index b6cc53ba980c..49de62cda598 100644
>>>>>>>> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>>>>>> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>>>>>> @@ -41,6 +41,7 @@ struct mlx5_vdpa_resources {
>>>>>>>> u32 pdn;
>>>>>>>> struct mlx5_uars_page *uar;
>>>>>>>> void __iomem *kick_addr;
>>>>>>>> + u64 phys_kick_addr;
>>>>>>>> u16 uid;
>>>>>>>> u32 null_mkey;
>>>>>>>> bool valid;
>>>>>>>> diff --git a/drivers/vdpa/mlx5/core/resources.c
b/drivers/vdpa/mlx5/core/resources.c
>>>>>>>> index 6521cbd0f5c2..665f8fc1710f 100644
>>>>>>>> --- a/drivers/vdpa/mlx5/core/resources.c
>>>>>>>> +++ b/drivers/vdpa/mlx5/core/resources.c
>>>>>>>> @@ -247,6 +247,7 @@ int
mlx5_vdpa_alloc_resources(struct mlx5_vdpa_dev *mvdev)
>>>>>>>> goto err_key;
>>>>>>>> kick_addr = mdev->bar_addr + offset;
>>>>>>>> + res->phys_kick_addr = kick_addr;
>>>>>>>> res->kick_addr = ioremap(kick_addr,
PAGE_SIZE);
>>>>>>>> if (!res->kick_addr) {
>>>>>>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>>>>>> index 10c5fef3c020..680751074d2a 100644
>>>>>>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>>>>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>>>>>> @@ -1865,8 +1865,14 @@ static void
mlx5_vdpa_free(struct vdpa_device *vdev)
>>>>>>>> static struct vdpa_notification_area
mlx5_get_vq_notification(struct vdpa_device *vdev, u16 idx)
>>>>>>>> {
>>>>>>>> + struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>>>>>>>> struct vdpa_notification_area ret = {};
>>>>>>>> + struct mlx5_vdpa_net *ndev;
>>>>>>>> +
>>>>>>>> + ndev = to_mlx5_vdpa_ndev(mvdev);
>>>>>>>> + ret.addr =
(phys_addr_t)ndev->mvdev.res.phys_kick_addr;
>>>>>>>> + ret.size = PAGE_SIZE;
>>>>>>> Note that the page will be mapped in to guest, so
it's only safe if the
>>>>>>> doorbeel exclusively own the page. This means if
there're other registers in
>>>>>>> the page, we can not let the doorbell bypass to
work.
>>>>>>>
>>>>>>> So this is suspicious at least in the case of
subfunction where we calculate
>>>>>>> the bar length in mlx5_sf_dev_table_create() as:
>>>>>>>
>>>>>>> table->sf_bar_length = 1 <<
(MLX5_CAP_GEN(dev, log_min_sf_size) + 12);
>>>>>>>
>>>>>>> It looks to me this can only work for the arch with
PAGE_SIZE = 4096,
>>>>>>> otherwise we can map more into the
userspace(guest).
>>>>>>>
>>>>>> Correct, so I guess I should return here 4096.
>>>> I'm not quite sure but since the calculation of the
sf_bar_length is doen
>>>> via a shift of 12, it might be correct.
>>>>
>>>> And please double check if the doorbell own the page
exclusively.
>>> I am checking if it is safe to map the any part of the SF's BAR
to
>>> userspace without harming other functions. If this is true, I will
check
>>> if I can return PAGE_SIZE without compromising security.
>>
>> It's usally not safe and a layer violation if other registers are
placed at
>> the same page.
>>
>>
>>> I think we may
>>> need to extend struct vdpa_notification_area to contain another
field
>>> offset which indicates the offset from addr where the actual
doorbell
>>> resides.
>>
>> The movitiaton of the current design is to be fit seamless into how
Qemu
>> model doorbell layouts currently:
>>
>> 1) page-per-vq, each vq has its own page aligned doorbell
>> 2) 2 bytes doorbell, each vq has its own 2 byte aligend doorbell
>>
>> Only 1) is support in vhost-vDPA (and vhost-user) since it's rather
simple
>> and secure (page aligned) to be modelled and implemented via mmap().
>>
>> Exporting a complex layout is possbile but requires careful design.
>>
>> Actually, we had antoher option
>>
>> 3) shared doorbell: all virtqueue shares a single page aligned doorbell
>>
> This nearly matches we have in ConnectX devices. All the doorbells are
> located at the same place. For 4K page size atchitectures it is aligned
> to the start of the page. For larger page sizes it is not aligned.
> If we don't allow to some offset within the page, it means that direct
> doorbells will not work for 64K page size archs over ConnectX.
Right, just to clarify. This can still be model by the current
page-per-vq model. It means the doorbell will be mapped into different
pages for each virtqueue by Qemu. So from the view of Qemu or guest,
each virtqueue has its own doorbell in this case.
>
>> This is not yet supported by Qemu.
For "not supported" I meant present this (doorbells sharing) layout to
guest.
Thanks
>>
>> Thanks
>>
>>
>>>>>> I also think that the check in vhost_vdpa_mmap() should
verify that the
>>>>>> returned size is not smaller than PAGE_SIZE because the
returned address
>>>>> Actually I think it's ok since you verify the size
equals vma->vm_end -
>>>>> vma->vm_start which must be at least PAGE_SIZE.
>>>> Yes.
>>>>
>>>> Thanks
>>>>
>>>>
>>>>>> might just be aligned to PAGE_SIZE. I think this should
be enoght but
>>>>>> maybe also use the same logic in vhost_vdpa_fault().