Re: [PATCH v3 1/3] arm64: kvm: support kvmtool to detect RAS extension feature

[gengdongjiu]

Dear James,

>
>  Hi Dongjiu Geng,
>
> On 30/04/17 06:37, Dongjiu Geng wrote:
>> Handle kvmtool's detection for RAS extension, because sometimes
>> the APP needs to know the CPU's capacity
>
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index d9e9697..1004039 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -64,6 +64,14 @@ static bool cpu_has_32bit_el1(void)
>>   return !!(pfr0 & 0x20);
>>  }
>>
>> +static bool kvm_arm_support_ras_extension(void)
>> +{
>> + u64 pfr0;
>> +
>> + pfr0 = read_system_reg(SYS_ID_AA64PFR0_EL1);
>> + return !!(pfr0 & 0x10000000);
>> +}
>
> Why are we telling user-space that the CPU has RAS extensions? EL0 can't do
> anything with this and the guest EL1 can detect it from the id registers.
>
>
> Are you using this to decide whether or not to generate a HEST for the guest?

James, yes, it is.  my current user-space qemu EL0 patches indeed will
check the RAS  extensions.
if has the RAS extensions. for SEA, userspace qemu will generate the
CPER and inject the SEA to guest;
for SEI,  userspace qemu sets the virtual SEI with the specified
Syndrome(set the HCR_EL2.VSE and vsesr_el2 );
if not have RAS extensions, Qemu does nothing


>
> If Qemu/kvmtool supports handling memory-failure notifications from signals you
> should always generate a HEST. The GHES notification method could be anything
> Qemu can deliver to the guest using the KVM APIs. Notifications from Qemu to the
> guest don't depend on the RAS extensions. KVM has APIs for IRQ and SEA (you can
> use KVM_SET_ONE_REG).

I will consider your suggestion to  always generate a CPER instead of
relying on the RAS extensions, thanks
For this comments "SEA (you can use KVM_SET_ONE_REG)",  may be it will
be duplicated with the existed KVM API  as I mentioned in another mail
thread.I am considering that whether it is necessary to change the
vcpu registers in the Qemu/KVMTools

>
>
> I think we need a new API for injecting SError for SEI from Qemu/kvmtool, but it
> shouldn't be related to the RAS extensions. All v8.0 CPUs have HCR_EL2.VSE, so
> we need to know KVM supports this API.
>
> Your later patch adds code to set VSESR to make virtual RAS SErrors work, I
> think we need to expose that to user-space.
>
>
> Thanks,
>
> James