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Subject: RE: [virtio-comment] [PATCH 00/11] Introduce transitional mmr pci device
> From: Michael S. Tsirkin <mst@redhat.com> > Sent: Monday, April 3, 2023 1:49 PM > > Yes, but hypervisor is not involved in any configuration parsing or > > anything of that nature. > > It is only a passthrough fowarder from emulated IOBAR to memory mapped > > legacy registers. > > In other words, hypervisor do not care for the registers content at all. > > This part I do not see as important. legacy is frozen in time. Implement it once > and you are done. Datapath differences are more important. > > > > In other words, the guest doesn't know about Transitional MMR and > > > does not need any code changes. > > > > > > > 3. A hypervisor system prefers to have single stack regardless of > > > > virtio device type (net/blk) and be future compatible with a > > > > single vfio stack using SR-IOV or other scalable device > > > > virtualization technology to map PCI devices to the guest VM. > > > > (as transitional or otherwise) > > > > > > What does this paragraph mean? > > > > > It means regardless of a VF being transitional MMR VF or 1.x VF > > without any MMR extensions, there is single vfio virtio driver > > handling both type of devices to map to the guest VM. > > I don't think this can be vfio. You need a host layer translating things such as > device ID etc. > vfio layer does it. > > > > > > Modern devices were added to Linux in 2014 and support SR-IOV. > > > > > Why is it > > > important to support Transitional (which really means Legacy > > > devices, otherwise Modern devices would be sufficient)? > > > > > To support guest VMs which only understand legacy devices and > > unfortunately they are still in much wider use by the users. > > OK but supporting them with a passthrough driver such as vfio does not seem > that important. Not sure on what basis you assert it. I clarified in the cover letter that these are the user level requirements to support transitional and non-transitional devices both via single vfio subsystem.
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