linux-kernel - Re: [PATCH v1] vdpa/mlx5: Add support for doorbell bypassing

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Date:   Thu, 3 Jun 2021 15:49:04 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eli Cohen <elic@...dia.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] vdpa/mlx5: Add support for doorbell bypassing


在 2021/6/3 下午3:38, Eli Cohen 写道:
> On Thu, Jun 03, 2021 at 03:11:51PM +0800, Jason Wang wrote:
>> 在 2021/6/2 下午5:53, Eli Cohen 写道:
>>> Implement mlx5_get_vq_notification() to return the doorbell address.
>>> Since the notification area is mapped to userspace, make sure that the
>>> BAR size is at least PAGE_SIZE large.
>>>
>>> Signed-off-by: Eli Cohen <elic@...dia.com>
>>> ---
>>> v0 --> v1:
>>>     Make sure SF bar size is not smaller than PAGE_SIZE
>>>
>>>    drivers/vdpa/mlx5/core/mlx5_vdpa.h |  1 +
>>>    drivers/vdpa/mlx5/core/resources.c |  1 +
>>>    drivers/vdpa/mlx5/net/mlx5_vnet.c  | 17 +++++++++++++++++
>>>    3 files changed, 19 insertions(+)
>>>
>>> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>> index 09a16a3d1b2a..0002b2136b48 100644
>>> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>> @@ -42,6 +42,7 @@ 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 836ab9ef0fa6..d4606213f88a 100644
>>> --- a/drivers/vdpa/mlx5/core/resources.c
>>> +++ b/drivers/vdpa/mlx5/core/resources.c
>>> @@ -253,6 +253,7 @@ 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 5500bcfe84b4..1936039e05bd 100644
>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> @@ -1871,8 +1871,25 @@ 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;
>>> +	phys_addr_t addr;
>>> +
>>> +	/* If SF BAR size is smaller than PAGE_SIZE, do not use direct
>>> +	 * notification to avoid the risk of mapping pages that contain BAR of more
>>> +	 * than one SF
>>> +	 */
>>> +	if (MLX5_CAP_GEN(mvdev->mdev, log_min_sf_size) + 12 < PAGE_SHIFT)
>>> +		return ret;
>>> +
>>> +	ndev = to_mlx5_vdpa_ndev(mvdev);
>>> +	addr = (phys_addr_t)ndev->mvdev.res.phys_kick_addr;
>>> +	if (addr & ~PAGE_MASK)
>>> +		return ret;
>>
>> This has been checked by vhost-vDPA, and it's better to leave those policy
>> checking to them driver instead of checking it in the parent.
>>
> Not in all invocations of get_vq_notification(). For example, in
> vhost_vdpa_fault() you call remap_pfn_range() with notify.addr >>
> PAGE_SHIFT so it it was not aligned you mask this misalignment.


In order to have vhost_vdpa_fault() works, it should first pass the 
check of vhost_vdpa_mmap().

Othewise we won't install vma->vm_ops so there won't be a page fault for 
the doorbell.

Thanks


>
>> Thanks
>>
>>
>>> +	ret.addr = (phys_addr_t)ndev->mvdev.res.phys_kick_addr;
>>> +	ret.size = PAGE_SIZE;
>>>    	return ret;
>>>    }