Messages in this thread | | | From | Si-Wei Liu <> | Date | Wed, 28 Apr 2021 13:53:28 -0700 | Subject | Re: [PATCH] vdpa/mlx5: Add support for doorbell bypassing |
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On Sun, Apr 25, 2021 at 7:38 PM Jason Wang <jasowang@redhat.com> wrote: > > > 在 2021/4/25 下午9:25, Eli Cohen 写道: > > On Thu, Apr 22, 2021 at 04:59:11PM +0800, Jason Wang wrote: > >> 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 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.
So this is the proposed model for mlx5 vdpa with doorbell per-instance (rather than per-vq), assuming the exclusive ownership of mapped doorbell page?
> > > > > >> This is not yet supported by Qemu. > > > For "not supported" I meant present this (doorbells sharing) layout to > guest.
So it means this new layout perhaps will have to introduce new virtio features to guest thus not compatible with eixsting driver?
-Siwei > > 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(). >
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