linux-kernel - Re: [PATCH v5 12/18] kvm: arm64: Configure VTCR

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Date:   Thu, 20 Sep 2018 16:25:52 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Auger Eric <eric.auger@...hat.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        marc.zyngier@....com, cdall@...nel.org, pbonzini@...hat.com,
        rkrcmar@...hat.com, will.deacon@....com, catalin.marinas@....com,
        james.morse@....com, dave.martin@....com, julien.grall@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 12/18] kvm: arm64: Configure VTCR_EL2.SL0 per VM

Hi Eric,

On 20/09/18 15:25, Auger Eric wrote:
> Hi Suzuki,
> On 9/17/18 12:41 PM, Suzuki K Poulose wrote:
>> VTCR_EL2 holds the following key stage2 translation table
>> parameters:
>>    SL0  - Entry level in the page table lookup.
>>    T0SZ - Denotes the size of the memory addressed by the table.
>>
>> We have been using fixed values for the SL0 depending on the
>> page size as we have a fixed IPA size. But since we are about
>> to make it dynamic, we need to calculate the SL0 at runtime
>> per VM. This patch adds a helper to compute the value of SL0
>> for a VM based on the IPA size.
>>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Christoffer Dall <cdall@...nel.org>
>> Cc: Eric Auger <eric.auger@...hat.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>> Changes since v3:
>>   - Update reference to latest ARM ARM.
>>   - Update per-vm VTCR value of SL0.
>>   - Add helpers to decode levels from SL0.
>>   - Didn't pick up Reviewed-by tag from Eric, as there
>>     are some new changes in this version


(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
>> index 3fb1d440be6e..5c1487dc5dca 100644
>> --- a/arch/arm64/include/asm/kvm_arm.h
>> +++ b/arch/arm64/include/asm/kvm_arm.h
>> @@ -121,7 +121,6 @@
>>   #define VTCR_EL2_IRGN0_WBWA        TCR_IRGN0_WBWA
>>   #define VTCR_EL2_SL0_SHIFT 6
>>   #define VTCR_EL2_SL0_MASK  (3 << VTCR_EL2_SL0_SHIFT)
>> -#define VTCR_EL2_SL0_LVL1   (1 << VTCR_EL2_SL0_SHIFT)
>>   #define VTCR_EL2_T0SZ_MASK 0x3f
>>   #define VTCR_EL2_VS_SHIFT  19
>>   #define VTCR_EL2_VS_8BIT   (0 << VTCR_EL2_VS_SHIFT)
>> @@ -148,29 +147,59 @@
>>   /*
>>    * Stage2 translation configuration:
>>    * 64kB pages (TG0 = 1)
>> - * 2 level page tables (SL = 1)
>>    */
>> -#define VTCR_EL2_TGRAN_FLAGS                (VTCR_EL2_TG0_64K | VTCR_EL2_SL0_LVL1)
>> -#define VTTBR_X_TGRAN_MAGIC         38
>> +#define VTCR_EL2_TGRAN                      VTCR_EL2_TG0_64K
>> +#define VTCR_EL2_TGRAN_SL0_BASE             3UL
> the name if not obvious. I understand this is yet another magic number
> used in the formulae below:
> SL0(PAGE_SIZE, Entry_level) = SL0_BASE(PAGE_SIZE) - Entry_Level
> I first tried to map this onto some spec fields. May be worth a comment?

Sure, I will make that clear.


>
> Besides
> Reviewed-by: Eric Auger <eric.auger@...hat.com>

Thanks
Suzuki
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