linux-kernel - Re: [PATCH] KVM: arm64: Report Protected KVM cap only if KVM is enabled

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Date:   Fri, 09 Sep 2022 13:47:34 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Elliot Berman <quic_eberman@...cinc.com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, David Brazdil <dbrazdil@...gle.com>
Subject: Re: [PATCH] KVM: arm64: Report Protected KVM cap only if KVM is
 enabled

On 2022-09-09 13:44, Catalin Marinas wrote:
> On Thu, Sep 01, 2022 at 09:01:22PM -0700, Elliot Berman wrote:
>> If "kvm-arm.mode=protected" is present on kernel command line, but the
>> kernel doesn't actually support KVM because it booted from EL1, the
>> ARM64_KVM_PROTECTED_MODE capability is misleadingly reported as 
>> present.
>> Fix this by adding a check whether we booted from EL2.
>> 
>> Cc: Will Deacon <will@...nel.org>
>> Cc: David Brazdil <dbrazdil@...gle.com>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
>> ---
>>  arch/arm64/kernel/cpufeature.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/arm64/kernel/cpufeature.c 
>> b/arch/arm64/kernel/cpufeature.c
>> index 8d88433de81d..866667be0651 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -1974,7 +1974,7 @@ static void cpu_enable_mte(struct 
>> arm64_cpu_capabilities const *cap)
>>  #ifdef CONFIG_KVM
>>  static bool is_kvm_protected_mode(const struct arm64_cpu_capabilities 
>> *entry, int __unused)
>>  {
>> -	return kvm_get_mode() == KVM_MODE_PROTECTED;
>> +	return is_hyp_mode_available() && kvm_get_mode() == 
>> KVM_MODE_PROTECTED;
>>  }
>>  #endif /* CONFIG_KVM */
> 
> Could we not fix this in early_kvm_mode_cfg()?

That's be indeed preferable.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...