On Mon, Nov 04, 2024 at 04:30:17PM +0000, Peter Maydell wrote: > On Mon, 4 Nov 2024 at 15:34, Eric Auger <eric.au...@redhat.com> wrote:
[...] > > > If possible, it would be really helpful (and user-friendly) to be able > > > to specify the CPU feature names as you see under /proc/cpuinfo, and be > > > able to turn the flags on or off: > > > > > > -M virt -cpu franken,rndr=on,ts=on,fhm=off > > > > > > (... instead of specifying long system register IDs that groups together > > > a bunch of CPU features. If I understand it correctly, the register > > > "ID_AA64ISAR0_EL1" maps to a set of visible features listed here: > > > https://docs.kernel.org/arch/arm64/cpu-feature-registers.html) > > Not all the writable ID regs are visible through the above technique. > > But indeed I think we converged on the idea to use higher level feature > > names than ID reg field values. > > However we need to study the feasibility and mappings between those high > > level features and ID reg field values. > > The cons is that we need to describe this mapping manually. Besides > > being cumbersome this is also error prone. > > You might be interested in "Arm Architecture Features" on > https://developer.arm.com/Architectures/A-Profile%20Architecture#Downloads > which includes a 1.8MB Features.json which is a machine > readable version of the "what are the features and their > dependencies and ID registers and so on" information. I just took a quick at the JSON file. It was a bit difficult to get a sense of the structure of the file. Maybe it makes more sense to those who are more Arm-aware than me. Or maybe that's what you meant by "alpha quality" below :) Out of curiosity, I tried to find the features for the register "ID_AA64ISAR0_EL1". I was navigating via trial-and-error with `jq`. There's a lot of "right"/"left" traversing: $> jq '.parameters[136]|.constraints[1]|.right|.left|.value' Features.json "FEAT_TME" The register name is buried under this: $> jq '.parameters[136]|.constraints[1]|.right|.right|.left|.arguments' Features.json [ { "_type": "Types.Field", "value": { "field": "TME", "instance": null, "name": "ID_AA64ISAR0_EL1", "slices": null, "state": "AArch64" } } ] I was niavely expecting a more predictable structure such as: $> jq '.register[ID_AA64ISAR0_EL1]|.fields' Features.json FEAT_RNG FEAT_TLBIOS ... > But note that (a) it is alpha quality and (b) I am not personally > going to try to interpret what might be reasonable to do with it > based on the legal notice attached to it: that's a matter for > you and your lawyer ;-) Hmm, it sounds like until point (b) is clarified, this file is out of consideration from an upstream point of view. > -- PMM > -- /kashyap
