linux-kernel - Re: [PATCH v8 21/43] KVM: arm64: Handle realm VCPU load

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Message-ID: <0906c39b-2e67-4f5f-86fb-aa8d5abde0ed@arm.com>
Date: Wed, 21 May 2025 11:21:13 +0100
From: Steven Price <steven.price@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Joey Gouly <joey.gouly@....com>, Alexandru Elisei
 <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
 Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v8 21/43] KVM: arm64: Handle realm VCPU load

On 19/05/2025 18:48, Suzuki K Poulose wrote:
> On 16/04/2025 14:41, Steven Price wrote:
>> When loading a realm VCPU much of the work is handled by the RMM so only
>> some of the actions are required. Rearrange kvm_arch_vcpu_load()
>> slightly so we can bail out early for a realm guest.
>>
>> Signed-off-by: Steven Price <steven.price@....com>
>> Reviewed-by: Gavin Shan <gshan@...hat.com>
>> ---
>>   arch/arm64/kvm/arm.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index cf707130ef66..08d5e0d76749 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -644,10 +644,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu,
>> int cpu)
> 
> I think we use the pkvm hook to skip to the nommu goto, to avoid
> the VMID allocation and context flush.
> 
> 
>>       kvm_timer_vcpu_load(vcpu);
>>       kvm_vgic_load(vcpu);
>>       kvm_vcpu_load_debug(vcpu);
>> -    if (has_vhe())
>> -        kvm_vcpu_load_vhe(vcpu);
>> -    kvm_arch_vcpu_load_fp(vcpu);
>> -    kvm_vcpu_pmu_restore_guest(vcpu);
>>       if (kvm_arm_is_pvtime_enabled(&vcpu->arch))
>>           kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
> 
> We could also move thise pvtime to the bottom too ?
> 
>>   @@ -671,6 +667,15 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu,
>> int cpu)
>>                    &vcpu->arch.vgic_cpu.vgic_v3);
>>       }
>>   +    /* No additional state needs to be loaded on Realmed VMs */
>> +    if (vcpu_is_rec(vcpu))
>> +        return;
>> +
>> +    if (has_vhe())
>> +        kvm_vcpu_load_vhe(vcpu);
>> +    kvm_arch_vcpu_load_fp(vcpu);
>> +    kvm_vcpu_pmu_restore_guest(vcpu);
>> +
> 
> With the above addressed:
> 
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

Thanks, the suggestions above seem sensible, I'll make those changes.

Thanks,
Steve

> 
> 
>>       if (!cpumask_test_cpu(cpu, vcpu->kvm->arch.supported_cpus))
>>           vcpu_set_on_unsupported_cpu(vcpu);
>>   }
>