Re: [RFC 21/21] arm/cpu-features: Document custom vcpu model

[Cornelia Huck <cohuck@redhat.com>]

On Fri, Oct 25 2024, Daniel P. Berrangé <berrange@redhat.com> wrote:

> On Fri, Oct 25, 2024 at 03:28:35PM +0200, Eric Auger wrote:
>> Hi Daniel,
>> 
>> On 10/25/24 15:13, Daniel P. Berrangé wrote:
>> > On Fri, Oct 25, 2024 at 12:17:40PM +0200, Eric Auger wrote:
>> >> From: Cornelia Huck <cohuck@redhat.com>
>> >>
>> >> Add some documentation for the custom model.
>> >>
>> >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> >> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
>> >> ---
>> >>  docs/system/arm/cpu-features.rst | 55 +++++++++++++++++++++++++++-----
>> >>  1 file changed, 47 insertions(+), 8 deletions(-)
>> >
>> >> @@ -167,6 +196,16 @@ disabling many SVE vector lengths would be quite verbose, the ``sve<N>`` CPU
>> >>  properties have special semantics (see "SVE CPU Property Parsing
>> >>  Semantics").
>> >>  
>> >> +The ``custom`` CPU model needs to be configured via individual ID register
>> >> +field properties, for example::
>> >> +
>> >> +  $ qemu-system-aarch64 -M virt -cpu custom,SYSREG_ID_AA64ISAR0_EL1_DP=0x0
>> >> +
>> >> +This forces ID_AA64ISAR0_EL1 DP field to 0.
>> > What is the "baseline" featureset implied by 'custom' ?
>> there is no baseline at the moment. By default this is a host
>> passthrough model.
>
> Why do we need to create "custom" at all, as opposed to just letting
> users toggle features on "-cpu host" ? 

We could consolidate that to the current "host" model, once we figure
out how to handle the currently already existing properties. Models
based on the different architecture extensions would probably be more
useable in the long run; maybe "custom" has a place for testing.