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Thu, 22 Apr 2021 03:27:04 +0000 Subject: Re: [PATCH] vdpa/mlx5: Add support for doorbell bypassing To: Jason Wang , Eli Cohen , mst@redhat.com Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20210421104145.115907-1-elic@nvidia.com> From: =?UTF-8?Q?Mika_Penttil=c3=a4?= Message-ID: Date: Thu, 22 Apr 2021 06:27:02 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [91.145.109.188] X-ClientProxiedBy: HE1PR05CA0136.eurprd05.prod.outlook.com (2603:10a6:7:28::23) To DBAPR03MB6630.eurprd03.prod.outlook.com (2603:10a6:10:194::6) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.121] (91.145.109.188) by HE1PR05CA0136.eurprd05.prod.outlook.com (2603:10a6:7:28::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4042.19 via Frontend Transport; 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>>       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). > > Thanks > > Is there support as of today (in qemu  or elsewhere) to use this mmap doorbell instead of the traditional kick. --Mika > >>       return ret; >>   } >