linux-kernel - Re: [PATCH v2 08/17] kvm: arm/arm64: Prepare for VM specific stage2 translations

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Message-ID: <c12f7bb9-2a9f-ae30-4d69-f3e229e04f7c@arm.com>
Date:   Fri, 27 Apr 2018 16:58:13 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Julien Grall <julien.grall@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     ard.biesheuvel@...aro.org, kvm@...r.kernel.org,
        marc.zyngier@....com, catalin.marinas@....com,
        punit.agrawal@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, kristina.martsenko@....com,
        pbonzini@...hat.com, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 08/17] kvm: arm/arm64: Prepare for VM specific stage2
 translations

On 27/04/18 16:22, Suzuki K Poulose wrote:
> On 26/04/18 14:35, Julien Grall wrote:
>> Hi Suzuki,
>>
>> On 27/03/18 14:15, Suzuki K Poulose wrote:
>>> Right now the stage2 page table for a VM is hard coded, assuming
>>> an IPA of 40bits. As we are about to add support for per VM IPA,
>>> prepare the stage2 page table helpers to accept the kvm instance
>>> to make the right decision for the VM. No functional changes.
> 
> 
>>> diff --git a/arch/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
>>> index 3ab8b37..c3f1f9b 100644
>>> --- a/arch/arm/include/asm/kvm_arm.h
>>> +++ b/arch/arm/include/asm/kvm_arm.h
>>> @@ -133,8 +133,7 @@
>>>    * space.
>>>    */
>>>   #define KVM_PHYS_SHIFT    (40)
>>> -#define KVM_PHYS_SIZE    (_AC(1, ULL) << KVM_PHYS_SHIFT)
>>> -#define KVM_PHYS_MASK    (KVM_PHYS_SIZE - _AC(1, ULL))
>>
>> I assume you are moving them to kvm_mmu.h in order to match the arm64 side, right? If so, would not it make sense to make KVM_PHYS_SHIFT with it?
>>
>> [...]
> 
> I am moving all the macros that depend on the "kvm" instance to kvm_mmu.h.
> I will see if I can move the KVM_PHYS_SHIFT without much trouble.

It looks like we can't do that easily. KVM_PHYS_SHIFT is used for KVM_T0SZ
on arm, even though that can be simply hard coded to avoid the dependency on
KVM_PHYS_SHIFT (like we did for arm64, T0SZ is defined to 24). I would leave it
as it is to avoid the noise.

Cheers
Suzuki