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

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Date:   Fri, 9 Sep 2022 13:44:15 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...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 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()?

-- 
Catalin