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Sun, 05 Sep 2021 23:37:09 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyRCwrPqlTT9EQxN6i2JahNEijC2yzlB8bw+tqErn2HIqi0obsj9A8iduK7E+CvdT1s7MMNSQ== X-Received: by 2002:a1c:1f8e:: with SMTP id f136mr9990653wmf.132.1630910229544; Sun, 05 Sep 2021 23:37:09 -0700 (PDT) Received: from redhat.com ([2.55.131.183]) by smtp.gmail.com with ESMTPSA id g1sm8586151wrb.27.2021.09.05.23.37.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Sep 2021 23:37:08 -0700 (PDT) Date: Mon, 6 Sep 2021 02:37:03 -0400 From: "Michael S. Tsirkin" To: Yongji Xie Subject: Re: [PATCH v13 05/13] vdpa: Add reset callback in vdpa_config_ops Message-ID: <20210906023131-mutt-send-email-mst@kernel.org> References: <20210831103634.33-1-xieyongji@bytedance.com> <20210831103634.33-6-xieyongji@bytedance.com> <20210906015524-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: kvm , virtualization , Christian Brauner , Will Deacon , Jonathan Corbet , joro@8bytes.org, Matthew Wilcox , Christoph Hellwig , Dan Carpenter , John Garry , Liu Xiaodong , linux-fsdevel@vger.kernel.org, Al Viro , Stefan Hajnoczi , songmuchun@bytedance.com, Jens Axboe , He Zhe , Greg KH , Randy Dunlap , linux-kernel , iommu@lists.linux-foundation.org, bcrl@kvack.org, netdev@vger.kernel.org, Joe Perches , Robin Murphy , Mika =?iso-8859-1?Q?Penttil=E4?= X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Mon, Sep 06, 2021 at 02:09:25PM +0800, Yongji Xie wrote: > On Mon, Sep 6, 2021 at 1:56 PM Michael S. Tsirkin 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 > > > > > > 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 Hmm. I don't see it. What exactly will happen? What prevents device from poking at memory after reset? Note that dma unmap in e.g. del_vqs happens too late. And what about e.g. interrupts? E.g. we have this: /* Virtqueues are stopped, nothing can use vblk->vdev anymore. */ vblk->vdev = NULL; and this is no longer true at this point. -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization