Re: [PATCH] hw/i386/cpu: remove default_cpu_version and simplify

[Zhao Liu]

+Daniel,

On Sun, Dec 08, 2024 at 12:18:10PM +0530, Ani Sinha wrote:
> Date: Sun,  8 Dec 2024 12:18:10 +0530
> From: Ani Sinha <anisinha@redhat.com>
> Subject: [PATCH] hw/i386/cpu: remove default_cpu_version and simplify
> X-Mailer: git-send-email 2.45.2
> 
> commit 0788a56bd1ae3 ("i386: Make unversioned CPU models be aliases")
> introduced 'default_cpu_version' for PCMachineClass. This created three
> categories of CPU models:
>  - Most unversioned CPU models would use version 1 by default.
>  - For machines 4.0.1 and older that do not support cpu model aliases, a
>    special default_cpu_version value of CPU_VERSION_LEGACY is used.
>  - It was thought that future machines would use the latest value of cpu
>    versions corresponding to default_cpu_version value of
>    CPU_VERSION_LATEST [1].
> 
> Unfortunately, all pc machines still use the default cpu version of 1 for
> unversioned cpu models. Only microvms use CPU_VERSION_LATEST.

Hi Ani,

So could we use CPU_VERSION_LATEST for other machines now?

Mapping unversioned cpu models to the latest version sounds like more
user friendly.

Regards,
Zhao

> This change cleans up the complicated logic around default_cpu_version
> including getting rid of default_cpu_version property itself. A couple of new
> flags are introduced, one for the legacy model for machines 4.0.1 and older
> and other for microvms. For older machines, a new pc machine property is
> introduced that separates pc machine versions 4.0.1 and older from the newer
> machines. 4.0.1 and older machines are scheduled to be deleted towards
> end of 2025 since they would be 6 years old by then. At that time, we can
> remove all logic around legacy cpus. Microvms are the only machines that
> continue to use the latest cpu version. If this changes later, we can
> remove all logic around x86_cpu_model_last_version(). Default cpu version
> for unversioned cpu models is hardcoded to the value 1 and applies
> unconditionally for all pc machine types of version 4.1 and above.
> 
> This change also removes all complications around CPU_VERSION_AUTO
> including removal of the value itself.
> 
> 1) See commit dcafd1ef0af227 ("i386: Register versioned CPU models")
> 
> CC: imammedo@redhat.com
> Signed-off-by: Ani Sinha <anisinha@redhat.com>