linux-kernel - Re: [PATCH 5/5] KVM: arm64: Define KVM_PHYS_SHIFT

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Date:   Tue, 10 Aug 2021 14:29:14 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] KVM: arm64: Define KVM_PHYS_SHIFT_MIN

On 2021-08-10 08:02, Anshuman Khandual wrote:
> Drop the hard coded value for the minimum IPA range i.e 32 bit. Instead
> define a macro KVM_PHYS_SHIFT_MIN which improves the code readability.
> 
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: James Morse <james.morse@....com>
> Cc: Alexandru Elisei <alexandru.elisei@....com>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: kvmarm@...ts.cs.columbia.edu
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/include/asm/kvm_mmu.h | 3 ++-
>  arch/arm64/kvm/reset.c           | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_mmu.h 
> b/arch/arm64/include/asm/kvm_mmu.h
> index b52c5c4b9a3d..716f999818d9 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -141,7 +141,8 @@ static __always_inline unsigned long
> __kern_hyp_va(unsigned long v)
>   * We currently support using a VM-specified IPA size. For backward
>   * compatibility, the default IPA size is fixed to 40bits.
>   */
> -#define KVM_PHYS_SHIFT	(40)
> +#define KVM_PHYS_SHIFT		(40)
> +#define KVM_PHYS_SHIFT_MIN	(32)
> 
>  #define kvm_phys_shift(kvm)		VTCR_EL2_IPA(kvm->arch.vtcr)
>  #define kvm_phys_size(kvm)		(_AC(1, ULL) << kvm_phys_shift(kvm))
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index cba7872d69a8..8dc8b4b9de37 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -369,7 +369,7 @@ int kvm_arm_setup_stage2(struct kvm *kvm, unsigned
> long type)
>  	phys_shift = KVM_VM_TYPE_ARM_IPA_SIZE(type);
>  	if (phys_shift) {
>  		if (phys_shift > kvm_ipa_limit ||
> -		    phys_shift < 32)
> +		    phys_shift < KVM_PHYS_SHIFT_MIN)
>  			return -EINVAL;
>  	} else {
>  		phys_shift = KVM_PHYS_SHIFT;

This is not a KVM property, but an architectural one. If you
want to replace it with something more readable, please
make it global to the whole of arm64 (ARM64_MIN_PARANGE?).

Thanks,

       M.
-- 
Jazz is not dead. It just smells funny...