linux-kernel - Re: [PATCH v3 07/20] kvm: arm/arm64: Prepare for VM specific stage2 translations

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Date:   Mon, 2 Jul 2018 11:25:36 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, james.morse@....com,
        cdall@...nel.org, eric.auger@...hat.com, julien.grall@....com,
        will.deacon@....com, catalin.marinas@....com,
        punit.agrawal@....com, qemu-devel@...gnu.org
Subject: Re: [PATCH v3 07/20] kvm: arm/arm64: Prepare for VM specific stage2
 translations

On 02/07/18 11:12, Marc Zyngier wrote:
> On 29/06/18 12:15, 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.
>> Adds stage2_pgd_size(kvm) to replace S2_PGD_SIZE. Also, moves
>> some of the definitions dependent on kvm instance to asm/kvm_mmu.h
>> for arm32. In that process drop the _AC() specifier constants
>>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Christoffer Dall <cdall@...nel.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>> Changes since V2:
>>   - Update commit description abuot the movement to asm/kvm_mmu.h
>>     for arm32
>>   - Drop _AC() specifiers
>> ---
>>   arch/arm/include/asm/kvm_arm.h                |   3 +-
>>   arch/arm/include/asm/kvm_mmu.h                |  15 +++-
>>   arch/arm/include/asm/stage2_pgtable.h         |  42 ++++-----
>>   arch/arm64/include/asm/kvm_mmu.h              |   7 +-
>>   arch/arm64/include/asm/stage2_pgtable-nopmd.h |  18 ++--
>>   arch/arm64/include/asm/stage2_pgtable-nopud.h |  16 ++--
>>   arch/arm64/include/asm/stage2_pgtable.h       |  49 ++++++-----
>>   virt/kvm/arm/arm.c                            |   2 +-
>>   virt/kvm/arm/mmu.c                            | 119 +++++++++++++-------------
>>   virt/kvm/arm/vgic/vgic-kvm-device.c           |   2 +-
>>   10 files changed, 148 insertions(+), 125 deletions(-)
>>
>> 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))
>> +
>>   #define PTRS_PER_S2_PGD	(_AC(1, ULL) << (KVM_PHYS_SHIFT - 30))
>>   
>>   /* Virtualization Translation Control Register (VTCR) bits */
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index 8553d68..f36eb20 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -36,15 +36,19 @@
>>   	})
>>   
>>   /*
>> - * KVM_MMU_CACHE_MIN_PAGES is the number of stage2 page table translation levels.
>> + * kvm_mmu_cache_min_pages() is the number of stage2 page
>> + * table translation levels, excluding the top level, for
>> + * the given VM. Since we have a 3 level page-table, this
>> + * is fixed.
> 
> I find this comment quite confusing: number of levels, but excluding the
> top one? The original one was just as bad, to be honest.
> 
> Can't we just say: "kvm_mmu_cache_min_page() is the number of pages
> required to install a stage-2 translation"?

Yes, that is much better.  Will change it.

>> diff --git a/arch/arm64/include/asm/stage2_pgtable.h b/arch/arm64/include/asm/stage2_pgtable.h
>> index 8b68099..057a405 100644
>> --- a/arch/arm64/include/asm/stage2_pgtable.h
>> +++ b/arch/arm64/include/asm/stage2_pgtable.h
>> @@ -65,10 +65,10 @@
>>   #define PTRS_PER_S2_PGD			(1 << (KVM_PHYS_SHIFT - S2_PGDIR_SHIFT))
>>   
>>   /*
>> - * KVM_MMU_CACHE_MIN_PAGES is the number of stage2 page table translation
>> + * kvm_mmmu_cache_min_pages is the number of stage2 page table translation
>>    * levels in addition to the PGD.
>>    */
>> -#define KVM_MMU_CACHE_MIN_PAGES		(STAGE2_PGTABLE_LEVELS - 1)
>> +#define kvm_mmu_cache_min_pages(kvm)	(STAGE2_PGTABLE_LEVELS - 1)
> 
> Same comment as for the 32bit case.
> 
>>   

>>
> 
> Otherwise:
> 
> Acked-by: Marc Zyngier <marc.zyngier@....com>

Thanks
Suzuki