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Thu, 22 Apr 2021 08:21:49 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-214.pek2.redhat.com [10.72.13.214]) by smtp.corp.redhat.com (Postfix) with ESMTP id 198EB63623; Thu, 22 Apr 2021 08:21:46 +0000 (UTC) Subject: Re: [PATCH] vdpa/mlx5: Add support for doorbell bypassing To: Eli Cohen Cc: mst@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20210421104145.115907-1-elic@nvidia.com> <20210422060358.GA140698@mtl-vdi-166.wap.labs.mlnx> <20210422080725.GB140698@mtl-vdi-166.wap.labs.mlnx> From: Jason Wang Message-ID: <9d3d8976-800d-bb14-0a4a-c4b008f6872c@redhat.com> Date: Thu, 22 Apr 2021 16:21:45 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <20210422080725.GB140698@mtl-vdi-166.wap.labs.mlnx> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>> --- >>>> 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 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().