linux-kernel - Re: [PATCH v3 2/6] KVM: arm64: maintain per VM value for CTR

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Date: Thu, 30 May 2024 13:24:01 +0200 (CEST)
From: Sebastian Ott <sebott@...hat.com>
To: Eric Auger <eauger@...hat.com>
cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
    linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>, 
    Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>, 
    Suzuki K Poulose <suzuki.poulose@....com>, 
    Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 2/6] KVM: arm64: maintain per VM value for CTR_EL0

On Wed, 29 May 2024, Eric Auger wrote:
> On 5/29/24 17:51, Sebastian Ott wrote:
>> On Wed, 29 May 2024, Eric Auger wrote:
>>>> @@ -3557,6 +3557,13 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
>>>>      struct kvm *kvm = vcpu->kvm;
>>>>      unsigned long i;
>>>>
>>>> +    if (!kvm_vcpu_initialized(vcpu))
>>> at this stage of the reading, why is the above check needed?
>>
>> To make sure that a later call to this function doesn't overwrite
>> the value provided by userspace. (See e016333745c "KVM: arm64: Only
>> reset vCPU-scoped feature ID regs once").
> but isn't it overwritten through the .reset=reset_ctr() that is
> populated in next patch?

No, this is done via reset_vcpu_ftr_id_reg() and also guarded by
kvm_vcpu_initialized().

Sebastian