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Tsirkin" To: Jason Wang Subject: Re: [PATCH] virtio_pci: Wait for legacy device to be reset Message-ID: <20230411024155-mutt-send-email-mst@kernel.org> References: <20230411013833.1305-1-angus.chen@jaguarmicro.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: "virtualization@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , Angus Chen 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="utf-8" Content-Transfer-Encoding: base64 Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" T24gVHVlLCBBcHIgMTEsIDIwMjMgYXQgMDI6Mzk6MzRQTSArMDgwMCwgSmFzb24gV2FuZyB3cm90 ZToKPiBPbiBUdWUsIEFwciAxMSwgMjAyMyBhdCAyOjM24oCvUE0gQW5ndXMgQ2hlbiA8YW5ndXMu 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Tsirkin" To: Jason Wang Cc: Angus Chen , "virtualization@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] virtio_pci: Wait for legacy device to be reset Message-ID: <20230411024155-mutt-send-email-mst@kernel.org> References: <20230411013833.1305-1-angus.chen@jaguarmicro.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 11, 2023 at 02:39:34PM +0800, Jason Wang wrote: > On Tue, Apr 11, 2023 at 2:36 PM Angus Chen wrote: > > > > Hi. > > > > > -----Original Message----- > > > From: Jason Wang > > > Sent: Tuesday, April 11, 2023 1:24 PM > > > To: Angus Chen > > > Cc: mst@redhat.com; virtualization@lists.linux-foundation.org; > > > linux-kernel@vger.kernel.org > > > Subject: Re: [PATCH] virtio_pci: Wait for legacy device to be reset > > > > > > On Tue, Apr 11, 2023 at 9:39 AM Angus Chen > > > wrote: > > > > > > > > We read the status of device after reset, > > > > It is not guaranteed that the device be reseted successfully. > > > > We can use a while loop to make sure that,like the modern device did. > > > > The spec is not request it ,but it work. > > > > > > The only concern is if it's too late to do this. > > > > > > Btw, any reason you want to have a legacy hardware implementation. It > > > will be very tricky to work correctly. > > En,I found this in the real production environment some times about one year ago. > > and I fix this out of tree.our virtio card had been sold about thousands . > > > > Now,we created a new card, it support virtio 0.95,1.0,1.1 etc. > > And we use this host vdpa+ legacy virtio in vm to hot migration,we found that the > > Legacy model often get the middle state value after reset and probe again. > > The Soc is Simulated by fpga which is run slower than the host,so the same bug > > Is found more frequently when the host use the other kernel like ubuntu or centos8. > > > > So we hope we can fix this by upstream . > > I think you can do mediation in your hypervisor. > > When trapping set_status(), the hypervisor will not return until it > reads 0 from the hardware? > > Thanks Note that for legacy guests, 0 status write is not the only way to reset the device, writing 0 into pa is another. > > > > > > Thanks > > > > > > > > > > > Signed-off-by: Angus Chen > > > > --- > > > > drivers/virtio/virtio_pci_legacy.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c > > > > index 2257f1b3d8ae..f2d241563e4f 100644 > > > > --- a/drivers/virtio/virtio_pci_legacy.c > > > > +++ b/drivers/virtio/virtio_pci_legacy.c > > > > @@ -14,6 +14,7 @@ > > > > * Michael S. Tsirkin > > > > */ > > > > > > > > +#include > > > > #include "linux/virtio_pci_legacy.h" > > > > #include "virtio_pci_common.h" > > > > > > > > @@ -97,7 +98,8 @@ static void vp_reset(struct virtio_device *vdev) > > > > vp_legacy_set_status(&vp_dev->ldev, 0); > > > > /* Flush out the status write, and flush in device writes, > > > > * including MSi-X interrupts, if any. */ > > > > - vp_legacy_get_status(&vp_dev->ldev); > > > > + while (vp_legacy_get_status(&vp_dev->ldev)) > > > > + msleep(1); > > > > /* Flush pending VQ/configuration callbacks. */ > > > > vp_synchronize_vectors(vdev); > > > > } > > > > -- > > > > 2.25.1 > > > > > >