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

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Date:   Tue, 8 May 2018 12:16:48 +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 03/05/18 15:39, 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).
>> 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/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 596f8e4..9f3c8b8 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -392,10 +392,12 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>>   
>>   static inline void __cpu_init_stage2(void)
>>   {
>> -	u32 parange = kvm_call_hyp(__init_stage2_translation);
>> +	u32 ps;
>>   
>> -	WARN_ONCE(parange < 40,
>> -		  "PARange is %d bits, unsupported configuration!", parange);
>> +	kvm_call_hyp(__init_stage2_translation);
>> +	ps = id_aa64mmfr0_parange_to_phys_shift(read_sysreg(id_aa64mmfr0_el1));
> 
> Doesn't id_aa64mmfr0_parange_to_phys_shift() expect you do to the mask and shift
> for it? This will always hit the default case.

Good catch ! The error case was not hit on the system I tested, as it was
indeed having 48bit PA. I should have done more testing with Juno where it
is 40bit PA (which doesn't really allow different phys-shift ranges).

I will change the helper to extract the parange and the convert it.
Also, rename it to :

id_aa64mmfr0_phys_shift()

Cheers
Suzuki

> 
> 
>> +	WARN_ONCE(ps < 40,
>> +		  "PARange is %d bits, unsupported configuration!", ps);
>>   }
> 
> 
> 
> Thanks,
> 
> James
>