On Wed, 17 Jun 2020 08:28:24 +0000 "Tian, Kevin" <kevin.t...@intel.com> wrote:
> > From: Liu, Yi L <yi.l....@intel.com> > > Sent: Wednesday, June 17, 2020 2:20 PM > > > > > From: Jacob Pan <jacob.jun....@linux.intel.com> > > > Sent: Tuesday, June 16, 2020 11:22 PM > > > > > > On Thu, 11 Jun 2020 17:27:27 -0700 > > > Jacob Pan <jacob.jun....@linux.intel.com> wrote: > > > > > > > > > > > > > But then I thought it even better if VFIO leaves the entire > > > > > copy_from_user() to the layer consuming it. > > > > > > > > > OK. Sounds good, that was what Kevin suggested also. I just wasn't > > > > sure how much VFIO wants to inspect, I thought VFIO layer wanted to do > > > > a sanity check. > > > > > > > > Anyway, I will move copy_from_user to iommu uapi layer. > > > > > > Just one more point brought up by Yi when we discuss this offline. > > > > > > If we move copy_from_user to iommu uapi layer, then there will be > > multiple > > > copy_from_user calls for the same data when a VFIO container has > > multiple domains, > > > devices. For bind, it might be OK. But might be additional overhead for > > > TLB > > flush > > > request from the guest. > > > > I think it is the same with bind and TLB flush path. will be multiple > > copy_from_user. > > multiple copies is possibly fine. In reality we allow only one group per > nesting container (as described in patch [03/15]), and usually there > is just one SVA-capable device per group. > > > > > BTW. for moving data copy to iommy layer, there is another point which > > need to consider. VFIO needs to do unbind in bind path if bind failed, > > so it will assemble unbind_data and pass to iommu layer. If iommu layer > > do the copy_from_user, I think it will be failed. any idea? If a call into a UAPI fails, there should be nothing to undo. Creating a partial setup for a failed call that needs to be undone by the caller is not good practice. > This might be mitigated if we go back to use the same bind_data for both > bind/unbind. Then you can reuse the user object for unwinding. > > However there is another case where VFIO may need to assemble the > bind_data itself. When a VM is killed, VFIO needs to walk allocated PASIDs > and unbind them one-by-one. In such case copy_from_user doesn't work > since the data is created by kernel. Alex, do you have a suggestion how this > usage can be supported? e.g. asking IOMMU driver to provide two sets of > APIs to handle user/kernel generated requests? Yes, it seems like vfio would need to make use of a driver API to do this, we shouldn't be faking a user buffer in the kernel in order to call through to a UAPI. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
