Re: [PATCH v4 17/21] KVM: arm64: Save ESR_EL2 on guest SError

[Marc Zyngier <marc.zyngier@arm.com>]

On Tue, Oct 31 2017 at  4:26:01 am GMT, Marc Zyngier <marc.zyngier@arm.com> wrote:
> On Thu, Oct 19 2017 at  4:58:03 pm BST, James Morse <james.morse@arm.com> wrote:
>> When we exit a guest due to an SError the vcpu fault info isn't updated
>> with the ESR. Today this is only done for traps.
>>
>> The v8.2 RAS Extensions define ISS values for SError. Update the vcpu's
>> fault_info with the ESR on SError so that handle_exit() can determine
>> if this was a RAS SError and decode its severity.
>>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> ---
>>  arch/arm64/kvm/hyp/switch.c | 15 ++++++++++++---
>>  1 file changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
>> index af37658223a0..cba6d8ac105c 100644
>> --- a/arch/arm64/kvm/hyp/switch.c
>> +++ b/arch/arm64/kvm/hyp/switch.c
>> @@ -230,13 +230,20 @@ static bool __hyp_text __translate_far_to_hpfar(u64 far, u64 *hpfar)
>>  	return true;
>>  }
>>  
>> +static void __hyp_text __populate_fault_info_esr(struct kvm_vcpu *vcpu)
>> +{
>> +	vcpu->arch.fault.esr_el2 = read_sysreg_el2(esr);
>> +}
>> +
>>  static bool __hyp_text __populate_fault_info(struct kvm_vcpu *vcpu)
>>  {
>> -	u64 esr = read_sysreg_el2(esr);
>> -	u8 ec = ESR_ELx_EC(esr);
>> +	u8 ec;
>> +	u64 esr;
>>  	u64 hpfar, far;
>>  
>> -	vcpu->arch.fault.esr_el2 = esr;
>> +	__populate_fault_info_esr(vcpu);
>> +	esr = vcpu->arch.fault.esr_el2;
>> +	ec = ESR_ELx_EC(esr);
>>  
>>  	if (ec != ESR_ELx_EC_DABT_LOW && ec != ESR_ELx_EC_IABT_LOW)
>>  		return true;
>> @@ -325,6 +332,8 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>>  	 */
>>  	if (exit_code == ARM_EXCEPTION_TRAP && !__populate_fault_info(vcpu))
>>  		goto again;
>> +	else if (ARM_EXCEPTION_CODE(exit_code) == ARM_EXCEPTION_EL1_SERROR)
>> +		__populate_fault_info_esr(vcpu);
>>  
>>  	if (static_branch_unlikely(&vgic_v2_cpuif_trap) &&
>>  	    exit_code == ARM_EXCEPTION_TRAP) {
>
> With this patch, the only case were we don't save ESR_EL2 is when we
> take an interrupt. I think we should bite the bullet and make it
> slightly more streamlined, always saving ESR_EL2.

Otherwise, an alternative would be to write something like:

	if (ARM_EXCEPTION_CODE(exit_code) != ARM_EXCEPTION_IRQ)
        	vcpu->arch.fault.esr_el2 = read_sysreg_el2(esr);

which still avoids saving it, and is a lot more readable.

Thanks,

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