[PATCH] kvm: pass the virtual SEI syndrome to guest OS

[gengdongjiu]

On 2017/3/20 23:08, James Morse wrote:
> Hi Dongjiu Geng,
> 
> On 20/03/17 13:58, Marc Zyngier wrote:
>> On 20/03/17 12:28, gengdongjiu wrote:
>>> On 2017/3/20 19:24, Marc Zyngier wrote:
>>>> Please include James Morse on anything RAS related, as he's already
>>>> looking at related patches.
> 
> (Thanks Marc,)
> 
>>>> On 20/03/17 07:55, Dongjiu Geng wrote:
>>>>> In the RAS implementation, hardware pass the virtual SEI
>>>>> syndrome information through the VSESR_EL2, so set the virtual
>>>>> SEI syndrome using physical SEI syndrome el2_elr to pass to
>>>>> the guest OS
> 
> How does this work with firmware first?

I explained it in previous mail about the work flow.

when the Guest OS triggers an SEI, it will firstly trap to EL3 firmware, El3 firmware records the error
info to the APEI table, then copy the ESR_EL3 ELR_EL3 to ESR_EL2 ELR_EL2 and transfers control to the
hypervisor, hypervisor delegates the error exception to EL1 guest OS by setting HCR_EL2.VSE to 1 and pass the
virtual SEI syndrome through vsesr_el2. The EL1 guest OS check the DISR_EL1 syndrome information to decide to
terminate the application, or do some other recovery action. because the HCR_EL2.AMO is set, so in fact, read
DISR_EL1, it returns the VDISR_EL2. and VDISR_EL2 is loaded from VSESR_EL2, so here I pass the virtual SEI
syndrome vsesr_el2.

> If we took a Physical SError Interrupt the CPER records are in the hosts memory.
> To deliver a RAS event to the guest something needs to generate CPER records and
> put them in the guest memory. Only Qemu knows where these memory regions are.
> 
> Put another way, what is the guest expected to do with this SError interrupt?
No, we do not only panic,if it is EL0 application SEI. the OS error recovery
agent will terminate the EL0 application to isolate the error; If it is EL1 guest
OS SError, guest OS can see whether it can recover. if the error was in a read-only file cache buffer, guest OS
can invalidate the page and reload the data from disk.

if all of the above are failed, OS will panic.


> The only choice is panic(). We should send this via Qemu so that we can add
> proper guest RAS support later. Once Qemu has written the CPER records into
> guest memory, it can notify the guest.
> 
> Is anyone from Huawei looking at adding RAS support for Qemu?
 yes, I am looking at Qemu and want to add RAS support.
 do you mean let Qemu inject both the SEA and SEI?

> 
> 
> It looks like we should save/restore VSESR_EL2 as part of the guest CPU state,
> but this needs doing with the cpufeature framework so that the single-image
> kernel works on platforms with and without these features.
 yes, you are right, we will follow cpufeature framework.


> 
> Xie XiuQi's series for SEI also touches the cpufeature framework.
> 
> 
>>>>> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
>>>>> index aede1658aeda..770a153fb6ba 100644
>>>>> --- a/arch/arm64/kvm/hyp/switch.c
>>>>> +++ b/arch/arm64/kvm/hyp/switch.c
>>>>> @@ -86,6 +86,13 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
>>>>>  		isb();
>>>>>  	}
>>>>>  	write_sysreg(val, hcr_el2);
>>>>> +#ifdef CONFIG_HAS_RAS_EXTENSION
>>>>> +	/* If virtual System Error or Asynchronous Abort is pending. set
>>>>> +	 * the virtual exception syndrome information
>>>>> +	 */
>>>>> +	if (vcpu->arch.hcr_el2 & HCR_VSE)
> 
>>>>> +		write_sysreg(vcpu->arch.fault.vsesr_el2, vsesr_el2);
> 
> This won't build with versions of binutils that don't recognise vsesr_el2.
> Is there another patch out there that adds a sysreg definition for vsesr_el2?
> 
> 
>>>>> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
>>>>> index da6a8cfa54a0..08a13dfe28a8 100644
>>>>> --- a/arch/arm64/kvm/inject_fault.c
>>>>> +++ b/arch/arm64/kvm/inject_fault.c
>>>>> @@ -242,4 +242,14 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
>>>>>  void kvm_inject_vabt(struct kvm_vcpu *vcpu)
>>>>>  {
>>>>>  	vcpu_set_hcr(vcpu, vcpu_get_hcr(vcpu) | HCR_VSE);
>>>>> +#ifdef CONFIG_HAS_RAS_EXTENSION
>>>>> +	/* If virtual System Error or Asynchronous Abort is set. set
>>>>> +	 * the virtual exception syndrome information
>>>>> +	 */
>>>>> +	kvm_vcpu_set_vsesr(vcpu, ((kvm_vcpu_get_vsesr(vcpu)
>>>>> +				& (~VSESR_ELx_IDS_ISS_MASK))
>>>>> +				| (kvm_vcpu_get_hsr(vcpu)
>>>>> +				& VSESR_ELx_IDS_ISS_MASK)));
>>>>
>>>> What is the rational for setting VSESR_EL2 with the EL1 syndrome
>>>> information? That doesn't make any sense to me.
>>> thanks, I set the VSESR_EL2 using the  EL2 syndrome information, "kvm_vcpu_get_hsr"
>>> return the value of esr_el2, not EL1 syndrome information
>>
>> Ah, good point. But that doesn't make it more valid. I still don't see
>> anything in the spec that supports this behaviour, and I still propose
>> that when RAS is enabled, the VSError injection is mediated by userspace.
> 
> I agree, we should be handling RAS errors as firmware-first, and Qemu plays the
> part of firmware for a guest. We will probably need to have a KVM API for Qemu
> to pend an SError with a specific ESR value.
> 
> If this isn't a firmware-first RAS error the existing code will pend an SError
> for the guest.
> 
so for both SEA and SEI, do you prefer to below steps?
EL0/EL1 SEI/SEA ---> EL3 firmware first handle ------> EL2 hypervisor notify the Qemu to inject SEI/SEA------>Qemu call KVM API to inject SEA/SEI---->KVM inject SEA/SEI to guest OS


> 
> Thanks,
> 
> James
> 
> 
> .
>