On Thu, Nov 28, 2024 at 08:54:26AM -0400, Jason Gunthorpe wrote: > On Wed, Nov 27, 2024 at 08:44:47PM -0800, Nicolin Chen wrote: > > On Wed, Nov 27, 2024 at 11:29:06PM -0500, Donald Dutile wrote: > > > On 11/27/24 5:21 AM, Shameerali Kolothum Thodi wrote: > > > > > > W.r.t naming, maybe something related to "hardware-accelerated"? > > > > > > > > > > > Given that 'accel' has been used for hw-acceleration elsewhere, that > > > > > seems > > > > > like a reasonable 'mode'. > > > > > But, it needs a paramater to state was is being accelerated. > > > > > i.e., the more global 'accel=kvm' has 'kvm'. > > > > > > > > I was thinking more like calling this hw accelerated nested SMMUv3 > > > > emulation > > > > as 'smmuv3-accel'. This avoids confusion with the already existing > > > > 'iommu=smmuv3' that also has a nested emulation support. > > > > > > > > ie, > > > > -device arm-smmuv3-accel,id=smmuv1,bus=pcie.1 \ > > > > > > .. > > > I -think- you are saying below, that we have to think a bit more about > > > this > > > device tagging. I'm thinking more like > > > - device arm-smmuv3,accel=<vcmdq>,id=smmu1,bus=pcie.1 \ > > > > I wonder if we really need a "vcmdq" enabling/disabling option? > > > > Jason's suggested approach for a vIOMMU allocation is to retry- > > on-failure, so my draft patches allocate a TEGRA241_CMDQV type > > of vIOMMU first, and then fall back to a regular SMMUV3 type if > > it fails. So, a host that doesn't have a VCMDQ capability could > > still work with the fallback/default pathway. > > It needs to be configurable so the VM can be configured in a > consistent way across nodes > > autodetection of host features is nice for experimenting but scale > deployments should precisely specify every detail about the VM and not > rely on host detection. Otherwise the VM instance type will be ill > defined..
In that case, we'd need to expose a vcmdq capability somewhere. We do for vIOMMU via hw_info. Should we keep the consistency? Otherwise, some sysfs nodes (easier for libvirt) could do the job too: num_available_vintfs, max_vcmdqs_per_vintf, and etc. Thanks Nicolin
