linux-kernel - Re: [PATCH] arm64/mm: Fix __enable_mmu() for new TGRAN range values

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Message-ID: <20210309140527.GB28395@willie-the-truck>
Date:   Tue, 9 Mar 2021 14:05:28 +0000
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org,
        James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Fix __enable_mmu() for new TGRAN range values

On Mon, Mar 08, 2021 at 02:42:00PM +0000, Marc Zyngier wrote:
> On Fri, 05 Mar 2021 14:36:09 +0000,
> Anshuman Khandual <anshuman.khandual@....com> wrote:
> > -	switch (cpuid_feature_extract_unsigned_field(mmfr0, tgran_2)) {
> > -	default:
> > -	case 1:
> > +	tgran_2 = cpuid_feature_extract_unsigned_field(mmfr0, tgran_2_shift);
> > +	if (tgran_2 == ID_AA64MMFR0_TGRAN_2_SUPPORTED_NONE) {
> >  		kvm_err("PAGE_SIZE not supported at Stage-2, giving up\n");
> >  		return -EINVAL;
> > -	case 0:
> > +	} else if (tgran_2 == ID_AA64MMFR0_TGRAN_2_SUPPORTED_DEFAULT) {
> >  		kvm_debug("PAGE_SIZE supported at Stage-2 (default)\n");
> > -		break;
> > -	case 2:
> > +	} else if (tgran_2 >= ID_AA64MMFR0_TGRAN_2_SUPPORTED_MIN &&
> > +		   tgran_2 <= ID_AA64MMFR0_TGRAN_2_SUPPORTED_MAX) {
> >  		kvm_debug("PAGE_SIZE supported at Stage-2 (advertised)\n");
> > -		break;
> > +	} else {
> > +		kvm_err("Unsupported value, giving up\n");
> > +		return -EINVAL;
> 
> nit: this doesn't say *what* value is unsupported, and I really
> preferred the switch-case version, such as this:
> 
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 1f22b36a0eff..d267e4b1aec6 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -312,15 +312,18 @@ int kvm_set_ipa_limit(void)
>  
>  	switch (cpuid_feature_extract_unsigned_field(mmfr0, tgran_2)) {
>  	default:
> -	case 1:
> +	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_NONE:
>  		kvm_err("PAGE_SIZE not supported at Stage-2, giving up\n");
>  		return -EINVAL;
> -	case 0:
> +	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_DEFAULT:
>  		kvm_debug("PAGE_SIZE supported at Stage-2 (default)\n");
>  		break;
> -	case 2:
> +	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_MIN ... ID_AA64MMFR0_TGRAN_2_SUPPORTED_MAX:
>  		kvm_debug("PAGE_SIZE supported at Stage-2 (advertised)\n");
>  		break;
> +	default:
> +		kvm_err("Unsupported value for TGRAN_2, giving up\n");
> +		return -EINVAL;
>  	}
>  
>  	kvm_ipa_limit = id_aa64mmfr0_parange_to_phys_shift(parange);
> 
> 
> Otherwise:
> 
> Acked-by: Marc Zyngier <maz@...nel.org>

Anshuman -- please can you spin a v2 with the switch syntax as suggested
above by Marc?

Will