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

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Message-ID: <43c5ffa3-b3c5-9154-72b5-811eeb9ece8f@arm.com>
Date:   Tue, 10 Aug 2021 20:49:38 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Marc Zyngier <maz@...nel.org>
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 8/10/21 6:59 PM, Marc Zyngier wrote:
> 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

Architectural property which suggest the minimum physical address shift
supported on a platform, as indicated via ID_AA64MMFR0.PARANGE = 0x0 ?

> want to replace it with something more readable, please
> make it global to the whole of arm64 (ARM64_MIN_PARANGE?).

Sure, will do.