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

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

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>
> ---
>  target/arm/cpu-qom.h |  2 ++
>  target/arm/cpu.c     | 24 ++++++++++++++++++++++++
>  target/arm/cpu64.c   | 21 +++++++++++++++++++++
>  3 files changed, 47 insertions(+)
> 
> diff --git a/target/arm/cpu-qom.h b/target/arm/cpu-qom.h
> index a42495b..d135ff8 100644
> --- a/target/arm/cpu-qom.h
> +++ b/target/arm/cpu-qom.h
> @@ -33,6 +33,8 @@ struct arm_boot_info;
>  #define ARM_CPU_GET_CLASS(obj) \
>      OBJECT_GET_CLASS(ARMCPUClass, (obj), TYPE_ARM_CPU)
>  
> +#define TYPE_ARM_MAX_CPU "max-" TYPE_ARM_CPU
> +
>  /**
>   * ARMCPUClass:
>   * @parent_realize: The parent class' realize handler.
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 9304277..190da97 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -1628,6 +1628,27 @@ static void pxa270c5_initfn(Object *obj)
>      cpu->reset_sctlr = 0x00000078;
>  }
>  
> +#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?

Actually what seems cleaner is to move "any" features here, and kill the
"any" cpu, using "max" for this purpose.

> +    }
> +}
> +#endif
> +
>  #ifdef CONFIG_USER_ONLY
>  static void arm_any_initfn(Object *obj)
>  {
> @@ -1691,6 +1712,9 @@ static const ARMCPUInfo arm_cpus[] = {
>      { .name = "pxa270-b1",   .initfn = pxa270b1_initfn },
>      { .name = "pxa270-c0",   .initfn = pxa270c0_initfn },
>      { .name = "pxa270-c5",   .initfn = pxa270c5_initfn },
> +#ifndef TARGET_AARCH64
> +    { .name = "max",         .initfn = arm_max_initfn },
> +#endif

>  #ifdef CONFIG_USER_ONLY
>      { .name = "any",         .initfn = arm_any_initfn },
>  #endif

and we can remove the last 3 lines.

> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> index 670c07a..38dcf32 100644
> --- a/target/arm/cpu64.c
> +++ b/target/arm/cpu64.c
> @@ -28,6 +28,7 @@
>  #include "hw/arm/arm.h"
>  #include "sysemu/sysemu.h"
>  #include "sysemu/kvm.h"
> +#include "kvm_arm.h"
>  
>  static inline void set_feature(CPUARMState *env, int feature)
>  {
> @@ -212,6 +213,25 @@ static void aarch64_a53_initfn(Object *obj)
>      define_arm_cp_regs(cpu, cortex_a57_a53_cp_reginfo);
>  }
>  
> +/* -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-arm is defined in cpu.c;
> + * this only needs to handle 64 bits.
> + */
> +static void aarch64_max_initfn(Object *obj)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +
> +    if (kvm_enabled()) {
> +        kvm_arm_set_cpu_features_from_host(cpu);
> +    } else {
> +        aarch64_a57_initfn(obj);
> +        /* In future we might add feature bits here even if the
> +         * real-world A57 doesn't implement them.
> +         */
> +    }
> +}
> +
>  #ifdef CONFIG_USER_ONLY
>  static void aarch64_any_initfn(Object *obj)
>  {
> @@ -240,6 +260,7 @@ typedef struct ARMCPUInfo {
>  static const ARMCPUInfo aarch64_cpus[] = {
>      { .name = "cortex-a57",         .initfn = aarch64_a57_initfn },
>      { .name = "cortex-a53",         .initfn = aarch64_a53_initfn },
> +    { .name = "max",                .initfn = aarch64_max_initfn },
>  #ifdef CONFIG_USER_ONLY
>      { .name = "any",         .initfn = aarch64_any_initfn },
>  #endif
>