linux-kernel - Re: [PATCH v2 4/6] KVM: arm64: add emulation for CTR

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Message-ID: <29e7b97b-7a61-9b64-2c57-5a5d0e5f190e@redhat.com>
Date: Wed, 8 May 2024 17:17:25 +0200 (CEST)
From: Sebastian Ott <sebott@...hat.com>
To: Oliver Upton <oliver.upton@...ux.dev>
cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
    linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>, 
    James Morse <james.morse@....com>, 
    Suzuki K Poulose <suzuki.poulose@....com>, 
    Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2 4/6] KVM: arm64: add emulation for CTR_EL0 register

Hej Oliver,

On Wed, 1 May 2024, Oliver Upton wrote:
>> +static u64 reset_ctr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd)
>> +{
>> +	vcpu->kvm->arch.ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
>> +	return vcpu->kvm->arch.ctr_el0;
>> +}
>> +
>
> We definitely do not want this value to change across a vCPU reset, it
> should be handled like the other ID registers where they only get reset
> once for the VM lifetime.

Hm, maybe I'm misreading the code here but I don't think this is true
for existing regs e.g. CLIDR_EL1 or the stuff defined via ID_WRITABLE().

Sebastian