[PATCH] KVM: arm64: Report Protected KVM cap only if KVM is enabled

[PATCH] KVM: arm64: Report Protected KVM cap only if KVM is enabled

[Elliot Berman]

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@kernel.org>
Cc: David Brazdil <dbrazdil@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.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 */
 

base-commit: 0982c8d859f8f7022b9fd44d421c7ec721bb41f9
-- 
2.25.1


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

[Catalin Marinas]

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@kernel.org>
> Cc: David Brazdil <dbrazdil@google.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.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

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

[Marc Zyngier]

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@kernel.org>
>> Cc: David Brazdil <dbrazdil@google.com>
>> Cc: Marc Zyngier <maz@kernel.org>
>> Signed-off-by: Elliot Berman <quic_eberman@quicinc.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...

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