Warning on SME when manually onlining CPUs late.

[Richard Henderson]

On 7/27/23 03:21, Jonathan Cameron wrote:
> Hi Mark
> 
> Hit this due to a silly config error on a QEMU TCG test but seemed worth asking about
> as I'm buried in other stuff and no time to investigate further for a few weeks.
> 
> Test probably could be simplified but it's more or less vanilla upstream QEMU with
> -cpu max -smp 8 and kernel command line with maxcpus=4
> 
> echo 1 > /sys/bus/cpu/devices/cpu4/online
> 
> CPU features: SANITY CHECK: Unexpected variation in SYS_SMCR_EL1. Boot CPU: 0x0000000000000f, CPU4: 0x0000008000000f
> CPU features: Unsupported CPU feature variation detected.
> 
> If this is already well known, then sorry for noise. I've not been paying much attention
> to the SME work.
> 
> Looks like the FA64 bit isn't set for the CPU state of the boot CPU that is being compared
> - I guess a stale record somewhere being used for the comparison?
> 
> Could be an issue on QEMU side I guess - though from a quick look it all seemed to be
> correct there.  Just in case +CC Richard.

SMCR_EL1 is for the OS to configure -- if they have different values then that's a kernel 
bug.  I wouldn't expect this to be a QEMU problem.


r~