Re: [PATCH] KVM: arm64: Check cpu_has_spe() before initializing PMSCR_EL1 in VHE

[Leo Yan <leo.yan@arm.com>]

On Wed, Oct 08, 2025 at 10:20:58PM +0530, Mukesh Ojha wrote:

[...]

> > > To me, this smells a lot more like some sort of papering over a
> > > firmware bug. Why isn't SPE available the first place?
> > 
> > TF-a grants permission to non-secure world [1], only access from secure
> > world or realm will trap to EL3.
> > 
> > So yes, it would be good to check if any issue in firmware.
> 
> We have our own implementation of EL3 and not using TF-A.

If you don't fix your firmware, you won't be able to use Arm SPE with
the Linux kernel.

> I believe, we should check in a similar way as we are doing for nVHE
> case.
> 
> if (host_data_test_flag(HAS_SPE))
> 	write_sysreg_el1(0, SYS_PMSCR);

The document Documentation/arch/arm64/booting.rst does not state that
permission for Arm SPE is mandatory, and the SPE driver [2] can
tolerate the lack of permission. So I'm fine with applying your patch
to fix the boot issue.

Thanks,
Leo

[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/perf/arm_spe_pmu.c#n1084