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

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Message-ID: <CAMj-D2BS7UHLC3DGM5i7fSRsqDKHmLYg79UV7sT6yHGFy5aYfw@mail.gmail.com>
Date:   Fri, 5 May 2017 01:20:53 +0800
From:   gengdongjiu <gengdj.1984@...il.com>
To:     James Morse <james.morse@....com>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>, pbonzini@...hat.com,
        rkrcmar@...hat.com, linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, rjw@...ysocki.net,
        Len Brown <lenb@...nel.org>, matt@...eblueprint.co.uk,
        robert.moore@...el.com, lv.zheng@...el.com, nkaje@...eaurora.org,
        zjzhang@...eaurora.org, mark.rutland@....com,
        akpm@...ux-foundation.org, eun.taik.lee@...sung.com,
        Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
        labbott@...hat.com, shijie.huang@....com, rruigrok@...eaurora.org,
        paul.gortmaker@...driver.com, tn@...ihalf.com,
        Fu Wei <fu.wei@...aro.org>, rostedt@...dmis.org,
        bristot@...hat.com, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-efi@...r.kernel.org, devel@...ica.org,
        Suzuki.Poulose@....com, Punit Agrawal <punit.agrawal@....com>,
        astone@...hat.com, harba@...eaurora.org,
        Hanjun Guo <hanjun.guo@...aro.org>,
        John Garry <john.garry@...wei.com>,
        Shiju Jose <shiju.jose@...wei.com>, joe@...ches.com,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        gengdongjiu <gengdj.1984@...il.com>
Subject: Re: [PATCH v3 1/3] arm64: kvm: support kvmtool to detect RAS
 extension feature

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