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

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Date: Wed, 29 May 2024 17:51:01 +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

Hej Eric,

On Wed, 29 May 2024, Eric Auger wrote:
>>  static int set_clidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>>  		      u64 val)
>>  {
>> -	u64 ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
>>  	u64 idc = !CLIDR_LOC(val) || (!CLIDR_LOUIS(val) && !CLIDR_LOUU(val));
>> +	u64 ctr_el0 = vcpu->kvm->arch.ctr_el0;
>>
>>  	if ((val & CLIDR_EL1_RES0) || (!(ctr_el0 & CTR_EL0_IDC) && idc))
>>  		return -EINVAL;
> nit: you may update the function doc comment which the extra handling of
> CTR_EL0.

Hm, there's no extra handling of CTR_EL0 it just uses the emulated value.

>> @@ -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").

Sebastian