Messages in this thread | | | Subject | Re: [PATCH] vdpa/mlx5: Add support for doorbell bypassing | From | Jason Wang <> | Date | Thu, 22 Apr 2021 16:59:11 +0800 |
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在 2021/4/22 下午4:39, Eli Cohen 写道: > On Thu, Apr 22, 2021 at 04:21:45PM +0800, Jason Wang wrote: >> 在 2021/4/22 下午4:07, Eli Cohen 写道: >>> 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: >>>>> 在 2021/4/21 下午6:41, Eli Cohen 写道: >>>>>> 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@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 is not yet supported by Qemu.
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().
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