linux-kernel - Re: [PATCH v4 18/43] arm64: RME: Handle realm enter/exit

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Message-ID: <282a765a-3b42-4175-8d9f-58456d13a37d@arm.com>
Date: Thu, 22 Aug 2024 16:06:16 +0100
From: Steven Price <steven.price@....com>
To: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>, 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>,
 Suzuki K Poulose <suzuki.poulose@....com>, 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>
Subject: Re: [PATCH v4 18/43] arm64: RME: Handle realm enter/exit

On 22/08/2024 05:04, Aneesh Kumar K.V wrote:
> Steven Price <steven.price@....com> writes:
> 
> ....
> 
>> +static int rec_exit_ripas_change(struct kvm_vcpu *vcpu)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	struct realm *realm = &kvm->arch.realm;
>> +	struct realm_rec *rec = &vcpu->arch.rec;
>> +	unsigned long base = rec->run->exit.ripas_base;
>> +	unsigned long top = rec->run->exit.ripas_top;
>> +	unsigned long ripas = rec->run->exit.ripas_value & 1;
>> +	unsigned long top_ipa;
>> +	int ret = -EINVAL;
>> +
>> +	if (realm_is_addr_protected(realm, base) &&
>> +	    realm_is_addr_protected(realm, top - 1)) {
>> +		kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_page_cache,
>> +					   kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu));
>> +		write_lock(&kvm->mmu_lock);
>> +		ret = realm_set_ipa_state(vcpu, base, top, ripas, &top_ipa);
>> +		write_unlock(&kvm->mmu_lock);
>> +	}
>> +
>> +	WARN(ret && ret != -ENOMEM,
>> +	     "Unable to satisfy SET_IPAS for %#lx - %#lx, ripas: %#lx\n",
>> +	     base, top, ripas);
>> +
>> +	/* Exit to VMM to complete the change */
>> +	kvm_prepare_memory_fault_exit(vcpu, base, top_ipa - base, false, false,
>> +				      ripas == 1);
>> +
>> +	return 0;
>> +}
>> +
> 
> arch/arm64/kvm/rme-exit.c:100:6: warning: variable 'top_ipa' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>         if (realm_is_addr_protected(realm, base) &&
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/arm64/kvm/rme-exit.c:114:44: note: uninitialized use occurs here
>         kvm_prepare_memory_fault_exit(vcpu, base, top_ipa - base, false, false,
>                                                   ^~~~~~~

I'm not sure why I didn't notice this before, if the condition is false
then we're hitting the WARN (i.e. this shouldn't happen), but I should
fix that up to handle the situation better.

Steve