Re: [RFC PATCH 2/3] arm64: Add support for asymmetric AArch32 EL0 configurations

[Qais Yousef <qais.yousef@arm.com>]

On 10/09/20 10:39, Catalin Marinas wrote:
> On Thu, Oct 08, 2020 at 07:16:40PM +0100, Qais Yousef wrote:
> > diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h
> > index 7faae6ff3ab4..c920fa45e502 100644
> > --- a/arch/arm64/include/asm/cpu.h
> > +++ b/arch/arm64/include/asm/cpu.h
> > @@ -15,6 +15,7 @@
> >  struct cpuinfo_arm64 {
> >  	struct cpu	cpu;
> >  	struct kobject	kobj;
> > +	bool		aarch32_valid;
> 
> As I replied to Greg, I think we can drop this field entirely. But, of
> course, please check that the kernel doesn't get tainted if booting on a
> non-32-bit capable CPU.

Faking asymmetry on Juno where CPU0 (boot CPU) is not 32bit capable

	dmesg | grep -i taint

returns nothing.

> 
> >  void cpuinfo_store_cpu(void)
> >  {
> >  	struct cpuinfo_arm64 *info = this_cpu_ptr(&cpu_data);
> >  	__cpuinfo_store_cpu(info);
> > +	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
> > +		__cpuinfo_store_cpu_32bit(info);

 >>>>>>>

> > +	/*
> > +	 * With asymmetric AArch32 support, populate the boot CPU information
> > +	 * on the first 32-bit capable secondary CPU if the primary one
> > +	 * skipped this step.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_ASYMMETRIC_AARCH32) &&
> > +	    !boot_cpu_data.aarch32_valid &&
> > +	    id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) {
> > +		__cpuinfo_store_cpu_32bit(&boot_cpu_data);
> > +		init_cpu_32bit_features(&boot_cpu_data);
> > +	}

<<<<<<<

> 
> Same here, we can probably drop the boot_cpu_data update here.

Removed the block above.

> 
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 077293b5115f..0b9aaee1df59 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -1131,6 +1131,16 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> >  		if (!vcpu_has_sve(vcpu))
> >  			val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
> >  		val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT);
> > +
> > +		if (!system_supports_sym_32bit_el0()) {
> > +			/*
> > +			 * We could be running on asym aarch32 system.
> > +			 * Override to present a aarch64 only system.
> > +			 */
> > +			val &= ~(0xfUL << ID_AA64PFR0_EL0_SHIFT);
> > +			val |= (ID_AA64PFR0_EL0_64BIT_ONLY << ID_AA64PFR0_EL0_SHIFT);
> > +		}
> 
> With the sanitised registers using the lowest value of this field, I
> think we no longer need this explicit masking.

Indeed. Removed.

Thanks

--
Qais Yousef