Re: [Qemu-devel] [PATCH 4/6] target/arm: Add "-cpu max" support

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 01/26/2018 11:33 AM, Peter Maydell wrote:
> On 26 January 2018 at 14:29, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>> Hi Peter,
>>
>> On 12/07/2017 03:14 PM, Peter Maydell wrote:
>>> Add support for "-cpu max" for ARM guests. This CPU type behaves
>>> like "-cpu host" when KVM is enabled, and like a system CPU with
>>> the maximum possible feature set otherwise. (Note that this means
>>> it won't be migratable across versions, as we will likely add
>>> features to it in future.)
>>>
>>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>>> ---
> 
>>> +#ifndef TARGET_AARCH64
>>> +/* -cpu max: if KVM is enabled, like -cpu host (best possible with this host);
>>> + * otherwise, a CPU with as many features enabled as our emulation supports.
>>> + * The version of '-cpu max' for qemu-system-aarch64 is defined in cpu64.c;
>>> + * this only needs to handle 32 bits.
>>> + */
>>> +static void arm_max_initfn(Object *obj)
>>> +{
>>> +    ARMCPU *cpu = ARM_CPU(obj);
>>> +
>>> +    if (kvm_enabled()) {
>>> +        kvm_arm_set_cpu_features_from_host(cpu);
>>> +    } else {
>>> +        cortex_a15_initfn(obj);> +        /* In future we might add feature bits here even if the
>>> +         * real-world A15 doesn't implement them.
>>> +         */
>>
>> Why not use arm_any_initfn() here?
> 
> That function (and the 'any' cpu) are deliberately only
> included in the linux-user binaries, not the system-emulation binaries.

why not use the V8 features?

> (Also arm_any_initfn() only initializes userspace-visible stuff, it
> doesn't provide ID register values etc for kernel-visible things.)

I'd still use an unique arm_max_initfn() such

  // initializes userspace-visible stuff
#ifndef CONFIG_USER_ONLY
  // initializes kernel-visible things
#endif

> 
>> Actually what seems cleaner is to move "any" features here, and kill the
>> "any" cpu, using "max" for this purpose.
> 
> We can't kill 'any', that would break back-compatibility
> of command lines.

and use an alias for 'any' -> 'max' or just

  { .name = "any", .initfn = arm_max_initfn }, /* backward compat */

Anyway:
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> 
> thanks
> -- PMM
>