linux-kernel - Re: [PATCH v2 11/17] kvm: arm64: Configure VTCR per VM

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Date:   Tue, 3 Apr 2018 16:44:07 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     James Morse <james.morse@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        cdall@...nel.org, marc.zyngier@....com, punit.agrawal@....com,
        will.deacon@....com, catalin.marinas@....com, pbonzini@...hat.com,
        rkrcmar@...hat.com, ard.biesheuvel@...aro.org,
        peter.maydell@...aro.org, kristina.martsenko@....com,
        mark.rutland@....com
Subject: Re: [PATCH v2 11/17] kvm: arm64: Configure VTCR per VM

On 03/04/18 15:58, James Morse wrote:
> Hi Suzuki,
> 
> On 27/03/18 14:15, Suzuki K Poulose wrote:
>> We set VTCR_EL2 very early during the stage2 init and don't
>> touch it ever. This is fine as we had a fixed IPA size. This
>> patch changes the behavior to set the VTCR for a given VM,
>> depending on its stage2 table. The common configuration for
>> VTCR is still performed during the early init as we have to
>> retain the hardware access flag update bits (VTCR_EL2_HA)
>> per CPU (as they are only set for the CPUs which are capabile).
> 
> (Nit: capable)
> 

Thanks for spotting, will fix it.

> 
>> The bits defining the number of levels in the page table (SL0)
>> and and the size of the Input address to the translation (T0SZ)
>> are programmed for each VM upon entry to the guest.
> 
>> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
>> index 870f4b1..5ccd3ae 100644
>> --- a/arch/arm64/kvm/hyp/switch.c
>> +++ b/arch/arm64/kvm/hyp/switch.c
>> @@ -164,6 +164,12 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
>>   static void __hyp_text __activate_vm(struct kvm_vcpu *vcpu)
>>   {
>>   	struct kvm *kvm = kern_hyp_va(vcpu->kvm);
>> +	u64 vtcr = read_sysreg(vtcr_el2);
>> +
>> +	vtcr &= ~VTCR_EL2_PRIVATE_MASK;
>> +	vtcr |= VTCR_EL2_SL0(kvm_stage2_levels(kvm)) |
>> +		VTCR_EL2_T0SZ(kvm_phys_shift(kvm));
>> +	write_sysreg(vtcr, vtcr_el2);
>>   	write_sysreg(kvm->arch.vttbr, vttbr_el2);
>>   }
> 
> Do we need to set this register for tlb maintenance too?
> e.g. tlbi for a 3-level-stage2 vm when a 2-level-stage2 vm's vtcr is loaded...
> 
> (The ARM-ARM has 'Any of the bits of VTCR_EL2 are permitted to be cached in a TLB'.)

You're right. We need to set the VTCR for the tlb operations. I think
we can do this by hooking it to the __tlb_switch_to_guest() routine.
Will address it in the next version.

Cheers
Suzuki