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

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Date:   Fri, 11 Oct 2019 14:33:43 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        rnayak@...eaurora.org, suzuki.poulose@....com,
        catalin.marinas@....com, 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
Subject: Re: Relax CPU features sanity checking on heterogeneous
 architectures

On Fri, 11 Oct 2019 11:50:11 +0100
Mark Rutland <mark.rutland@....com> 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:
> > 
> > [    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, at least at vcpu creation time (see kvm_reset_vcpu). But if one
of the !AArch32 CPU comes in late in the game (after we've started a
guest), all bets are off (we'll schedule the 32bit guest on that CPU,
enter the guest, immediately take an Illegal Exception Return, and
return to userspace with KVM_EXIT_FAIL_ENTRY).

Not sure we could do better, given the HW. My preference would be to
fail these CPUs if they aren't present at boot time.

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