From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7985EC433B4 for ; Fri, 30 Apr 2021 06:31:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 534CE6140C for ; Fri, 30 Apr 2021 06:31:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230284AbhD3GcR (ORCPT ); Fri, 30 Apr 2021 02:32:17 -0400 Received: from mga01.intel.com ([192.55.52.88]:16014 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229482AbhD3GcQ (ORCPT ); Fri, 30 Apr 2021 02:32:16 -0400 IronPort-SDR: znuy7+9FuX3kLqurB5DM/4/tFzQvoWyMok4pb9pdzk7CPl1HW98aC7hI8vOzquDRIflKLIIrSx jWTgY1gIMwnQ== X-IronPort-AV: E=McAfee;i="6200,9189,9969"; a="217946662" X-IronPort-AV: E=Sophos;i="5.82,260,1613462400"; d="scan'208";a="217946662" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Apr 2021 23:31:28 -0700 IronPort-SDR: DEpKX/quVAJUECcz1EuKcdOe+V3ayUdpQ7HlQm3KFF6bK7lj5x8u/Mx0NdAMlw3x5MVk/32r7k wfFoAS2Yl/rA== X-IronPort-AV: E=Sophos;i="5.82,260,1613462400"; d="scan'208";a="431269262" Received: from lingshan-mobl5.ccr.corp.intel.com (HELO [10.254.210.192]) ([10.254.210.192]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Apr 2021 23:31:26 -0700 Subject: Re: [PATCH] vdpa/mlx5: Add support for doorbell bypassing To: Jason Wang , 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> <9d3d8976-800d-bb14-0a4a-c4b008f6872c@redhat.com> <20210422083902.GA146406@mtl-vdi-166.wap.labs.mlnx> <20210429100033.GA215200@mtl-vdi-166.wap.labs.mlnx> From: "Zhu, Lingshan" Message-ID: <836263af-6791-0bd3-22c7-22197da021e9@intel.com> Date: Fri, 30 Apr 2021 14:31:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/30/2021 12:40 PM, Jason Wang wrote: > > 在 2021/4/29 下午6:00, 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 >>>>>>>>> --- >>>>>>>>>      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 >> I am not sure how this could solve the problem of 64KB archs. >> The point is that in ConnectX devices, the virtio queue objects doorbell >> is aligned to 4K. For larger system page sizes, the doorbell may not be >> aligned to a system page. >> So it seems not too complex to introduce offset within the page. > > > Three major issues: > > 1) single mmap() works at page level, it means we need map 64K to > guest and we can only do this safely if no other registers are placed > into the same page > 2) new uAPI to let the userspace know the offset > 3) how to model them with the virtio-pci in Qemu, and this may > introduce burdens for management (need some changes in the qemu > command line) to deal with the migration compatibility > > So consider the complexity, we can just stick to the current code. > That means mmap() will fail and qemu will keep using the eventfd based > kick. There is another case, mmap() works at page level, page size is at least 4K. Consider if a device has a bar containing the shared doorbell page at its last 4K space. In this bar layout, map a arch.page_size=64K page to usersapce would lead to fatal errors. I think we can assign the actual size of the doorbell area size to vdpa_notification.size than arch.page_size to avoid such issues. Then upper layers like vhost_vdpa should check whether this size can work with the machine arch and its alignment, if not, should fail over to use eventfd. Then do we still need a uAPI tell the offset within the page? Thanks Zhu Lingshan > > > >> >> BTW, for now, I am going to send another patch that makes sure page >> boundaries are not vilated. It requires some support from mlx5_core >> which is currently being reviewed internally. > > > Sure. > > Thanks > > >> >>> 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(). >