Re: [RFC 18/21] arm/cpu: Introduce a customizable kvm host cpu model

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Oct 25, 2024 at 12:17:37PM +0200, Eric Auger wrote:
> This new cpu model takes by default the host cpu values.
> However it exposes uint64 SYSREG properties for writable ID reg
> fields exposed by the host kernel. Properties are named
> SYSREG_<REG>_<FIELD> with REG and FIELD being those used
> in linux arch/arm64/tools/sysreg. This done by matching the
> writable fields retrieved from the host kernel against the
> generated description of sysregs.
> 
> An example of invocation is:
> -cpu custom,SYSREG_ID_AA64ISAR0_EL1_DP=0x0
> which sets DP field of ID_AA64ISAR0_EL1 to 0.

"SYSREG_" feels kinda redundant to repeat on every single
feature. 

Also, is this naming convention really the same one that users
will see when they look at /proc/cpuinfo to view features ? It
feels pretty low level to me ?  Naming after the registers &
fields, would be like configuring x86 CPU features by asking
for "SYSREG_EAX_1_ECX_20" instead of saying "vmx" which is the
human friendly name.


> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> 
> ---
> 
> At the moment, the custom model does not support legacy options
> of the host cpu model. We need to understand what we do with those
> latter (SVE, ...). This means that related KVM ioctl are
> not called yet.

It will be pretty painful to have to use different feature
terminology for different CPU models. Everything in libvirt
assuming feature terminology varies per-arch, not per-CPU
model.


With regards,
Daniel
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