linux-kernel - Re: Relax CPU features sanity checking on heterogeneous architectures

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Message-ID: <c8491f4b91058ef018fb5b3b9ff457cd@codeaurora.org>
Date:   Fri, 18 Oct 2019 15:48:43 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
        rnayak@...eaurora.org, suzuki.poulose@....com,
        catalin.marinas@....com,
        linux-arm-kernel <linux-arm-kernel-bounces@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, jeremy.linton@....com,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        andrew.murray@....com, will@...nel.org, Dave.Martin@....com,
        linux-arm-kernel@...ts.infradead.org, marc.w.gonzalez@...e.fr,
        linux-arm-msm-owner@...r.kernel.org
Subject: Re: Relax CPU features sanity checking on heterogeneous architectures

On 2019-10-18 01:30, Stephen Boyd wrote:
> Quoting Sai Prakash Ranjan (2019-10-11 06:40:13)
>> On 2019-10-11 19:04, Marc Zyngier wrote:
>> > On Fri, 11 Oct 2019 18:47:39 +0530
>> > Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org> wrote:
>> >
>> >> Hi Mark,
>> >>
>> >> Thanks a lot for the detailed explanations, I did have a look at all
>> >> the variations before posting this.
>> >>
>> >> On 2019-10-11 16:20, Mark Rutland wrote:
>> >> > Hi,
>> >> >
>> >> > On Fri, Oct 11, 2019 at 11:19:00AM +0530, Sai Prakash Ranjan wrote:
>> >> >> On latest QCOM SoCs like SM8150 and SC7180 with big.LITTLE arch, below
>> >> >> warnings are observed during bootup of big cpu cores.
>> >> >
>> >> > For reference, which CPUs are in those SoCs?
>> >> >
>> >>
>> >> SM8150 is based on Cortex-A55(little cores) and Cortex-A76(big cores).
>> >> I'm afraid I cannot give details about SC7180 yet.
>> >>
>> >> >> SM8150:
>> >> >> >> [    0.271177] CPU features: SANITY CHECK: Unexpected variation in
>> >> >> SYS_ID_AA64PFR0_EL1. Boot CPU: 0x00000011112222, CPU4: >> 0x00000011111112
>> >> >
>> >> > The differing fields are EL3, EL2, and EL1: the boot CPU supports
>> >> > AArch64 and AArch32 at those exception levels, while the secondary only
>> >> > supports AArch64.
>> >> >
>> >> > Do we handle this variation in KVM?
>> >>
>> >> We do not support KVM.
>> >
>> > Mainline does. You don't get to pick and choose what is supported or
>> > not.
>> >
>> 
>> Ok thats good.
>> 
> 
> I want KVM on sc7180. How do I get it? Is something going to not work?

I meant KVM is not supported for downstream android case where we do not 
have kernel booting from EL2.
And obviously I am wrong because SC7180 is not for android, so my bad.
I think Mark R's question about handling KVM variation was for Marc Z 
not me :p

As for something not going to work, as Mark said this warning does 
indicate that 32 bit EL1 guests won't
be able to run on big CPU cores.

- Sai