Messages in this thread | | | Date | Mon, 20 Jan 2020 08:17:17 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: Relax CPU features sanity checking on heterogeneous architectures |
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Hi Mark,
On 2019-10-11 19:24, Mark Rutland wrote: > On Fri, Oct 11, 2019 at 02:33:43PM +0100, Marc Zyngier wrote: >> On Fri, 11 Oct 2019 11:50:11 +0100 >> Mark Rutland <mark.rutland@arm.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). > > Ouch. We certainly can't remove the warning untill we deal with that > somehow, then. > >> 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. > > I agree; I think we need logic to check the ID register fields against > their EXACT, {LOWER,HIGHER}_SAFE, etc rules regardless of whether we > have an associated cap. That can then abort a late onlining of a CPU > which violates those rules w.r.t. the finalised system value. > > I suspect that we may want to split the notion of > safe-for-{user,kernel-guest} in the feature tables, as if nothing else > it will force us to consider those cases separately when adding new > stuff. >
I can help with testing these if you have any sample patches.
Thanks, Sai
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