On Thu, Apr 12, 2018 at 03:38:50PM +0800, Jason Wang wrote: > On 2018年04月12日 09:44, Tiwei Bie wrote: > > On Wed, Apr 11, 2018 at 08:37:17PM +0300, Michael S. Tsirkin wrote: > > > On Wed, Apr 11, 2018 at 04:38:53PM +0800, Tiwei Bie wrote: > > > > On Wed, Apr 11, 2018 at 04:01:19PM +0800, Jason Wang wrote: > > > > > On 2018年04月11日 15:20, Tiwei Bie wrote: > > > > > > This patch introduces VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB > > > > > > feature for vhost-user. By default, vhost-user backend needs > > > > > > to query the IOTLBs from QEMU after meeting unknown IOVAs. > > > > > > With this protocol feature negotiated, QEMU will provide all > > > > > > the IOTLBs to vhost-user backend without waiting for the > > > > > > queries from backend. This is helpful when using a hardware > > > > > > accelerator which is not able to handle unknown IOVAs at the > > > > > > vhost-user backend. > > > > > > > > > > > > Signed-off-by: Tiwei Bie<tiwei....@intel.com> > > > > > > --- > > > > > > The idea of this patch is to let QEMU push all the IOTLBs > > > > > > to vhost-user backend without waiting for the queries from > > > > > > the backend. Because hardware accelerator at the vhost-user > > > > > > backend may not be able to handle unknown IOVAs. > > > > > > > > > > > > This is just a RFC for now. It seems that, it doesn't work > > > > > > as expected when guest is using kernel driver (To handle > > > > > > this case, it seems that some RAM regions' events also need > > > > > > to be listened). Any comments would be appreciated! Thanks! > > > > > Interesting, a quick question is why this is needed? Can we just use > > > > > exist > > > > > IOTLB update message? > > > > Yeah, we are still using the existing IOTLB update messages > > > > to send the IOTLB messages to backend. The only difference > > > > is that, QEMU won't wait for the queries before sending the > > > > IOTLB update messages. > > > So I have a concern with that, in that without any flow > > > control the socket buffer used by vhost-user might become > > > full. > > Each IOTLB update message needs a reply. So I think it > > won't happen. > > Is this what we've already done now? I don't find any statement on this in > vhost-user.txt? > > """ > * VHOST_USER_IOTLB_MSG > > Id: 22 > Equivalent ioctl: N/A (equivalent to VHOST_IOTLB_MSG message type) > Master payload: struct vhost_iotlb_msg > Slave payload: u64 > > Send IOTLB messages with struct vhost_iotlb_msg as payload. > Master sends such requests to update and invalidate entries in the > device > IOTLB. The slave has to acknowledge the request with sending zero as > u64 > payload for success, non-zero otherwise. > This request should be send only when VIRTIO_F_IOMMU_PLATFORM feature > has been successfully negotiated. > """
Yeah, it's what we've already done now. It's in the above statement you quoted: "The slave has to acknowledge the request with sending zero as u64 payload for success, non-zero otherwise." > > And you probably need to modify the following statement: > > """ > The master isn't expected to take the initiative to send IOTLB update > messages, > as the slave sends IOTLB miss messages for the guest virtual memory areas it > needs to access. > """ Yeah, you're right. Thanks! This statement needs some minor updates. Best regards, Tiwei Bie > > Thanks > > > > > > Best regards, > > Tiwei Bie > > >
