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

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Date:   Tue, 10 Aug 2021 16:32:00 +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 16:19, Anshuman Khandual wrote:
> 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 ?

That's the one.

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