Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210831103634.33-1-xieyongji@bytedance.com> <20210831103634.33-6-xieyongji@bytedance.com>
 <20210906015524-mutt-send-email-mst@kernel.org>
In-Reply-To: <20210906015524-mutt-send-email-mst@kernel.org>
From:   Yongji Xie <xieyongji@bytedance.com>
Date:   Mon, 6 Sep 2021 14:09:25 +0800
Message-ID: <CACycT3v4ZVnh7DGe_RtAOx4Vvau0km=HWyCM=KzKhD+ahYKafQ@mail.gmail.com>
Subject: Re: [PATCH v13 05/13] vdpa: Add reset callback in vdpa_config_ops
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Jason Wang <jasowang@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Parav Pandit <parav@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christian Brauner <christian.brauner@canonical.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jens Axboe <axboe@kernel.dk>, bcrl@kvack.org,
        Jonathan Corbet <corbet@lwn.net>,
        =?UTF-8?Q?Mika_Penttil=C3=A4?= <mika.penttila@nextfour.com>,
        Dan Carpenter <dan.carpenter@oracle.com>, joro@8bytes.org,
        Greg KH <gregkh@linuxfoundation.org>,
        He Zhe <zhe.he@windriver.com>,
        Liu Xiaodong <xiaodong.liu@intel.com>,
        Joe Perches <joe@perches.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Will Deacon <will@kernel.org>,
        John Garry <john.garry@huawei.com>, songmuchun@bytedance.com,
        virtualization <virtualization@lists.linux-foundation.org>,
        netdev@vger.kernel.org, kvm <kvm@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Sep 6, 2021 at 1:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Aug 31, 2021 at 06:36:26PM +0800, Xie Yongji wrote:
> > This adds a new callback to support device specific reset
> > behavior. The vdpa bus driver will call the reset function
> > instead of setting status to zero during resetting.
> >
> > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
>
>
> This does gloss over a significant change though:
>
>
> > ---
> > @@ -348,12 +352,12 @@ static inline struct device *vdpa_get_dma_dev(struct vdpa_device *vdev)
> >       return vdev->dma_dev;
> >  }
> >
> > -static inline void vdpa_reset(struct vdpa_device *vdev)
> > +static inline int vdpa_reset(struct vdpa_device *vdev)
> >  {
> >       const struct vdpa_config_ops *ops = vdev->config;
> >
> >       vdev->features_valid = false;
> > -     ops->set_status(vdev, 0);
> > +     return ops->reset(vdev);
> >  }
> >
> >  static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
>
>
> Unfortunately this breaks virtio_vdpa:
>
>
> static void virtio_vdpa_reset(struct virtio_device *vdev)
> {
>         struct vdpa_device *vdpa = vd_get_vdpa(vdev);
>
>         vdpa_reset(vdpa);
> }
>
>
> and there's no easy way to fix this, kernel can't recover
> from a reset failure e.g. during driver unbind.
>

Yes, but it should be safe with the protection of software IOTLB even
if the reset() fails during driver unbind.

Thanks,
Yongji