On Mon, Jun 10, 2024 at 09:28:39PM -0300, Jason Gunthorpe wrote: > On Mon, Jun 10, 2024 at 04:04:30PM -0700, Nicolin Chen wrote: > > > > > Actually, even now as we put a dispatcher in VMM, VMM still does > > > > decode the CD table to link ASID to s1_hwpt. Otherwise, it could > > > > only broadcast a TLBI cmd to all pSMMUs. > > > > > > No, there should be no CD table decoding and no linking ASID to > > > anything by the VMM. > > > > > > The ARM architecture is clean, the ASID can remain private to the VM, > > > there is no reason for the VMM to understand it. > > > > But a guest-level TLBI command usually has only ASID available to > > know which pSMMU to dispatch the command. Without an ASID lookup > > table, how could VMM then dispatch a command to the corresponding > > pSMMU? > > It can broadcast. The ARM architecture does not expect a N:1 mapping > of SMMUs. This is why I think it is not such a good idea.. Hmm, I thought we had an agreed idea that we shouldn't broadcast a TLBI (except global NH_ALL/VAA) for invalidation performance? > Yes the VMM could walk the CD tables too and build up a bitmap of what > ASIDs are being used by what pSMMUs, and that would be fine for the > VMM to do, but I wouldn't necessarily recommend it :) CD table walkthrough would be always done only by VMM, while the lookup table could be created/maintained by the kernel. I feel a vasid table could make sense since we maintain the vdev_id table in the kernel space too. Anyway, it is still an implementation choice, as Kevin remarked. Thanks Nicolin
