Re: [PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception

[Marc Zyngier <maz@kernel.org>]

On Sat, 05 Oct 2024 15:14:21 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> On Sat, Oct 05, 2024 at 01:36:09PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
> 
> > > +	// PSTATE.EXLOCK is set to 0 upon any exception to a higher
> > > +	// EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
> > > +	// exception level.  See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
> > > +	if (kvm_has_gcs(vcpu->kvm) &&
> > > +	    (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
> > > +		u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
> 
> > No, please. This only works by luck when a guest has AArch32 EL0, and
> > creates more havoc on a NV guest. In general, this PSR_EL_MASK creates
> > more problem than anything else, and doesn't fit the rest of the code.
> 
> You say luck, I say careful architecture definition but sure.

I wasn't talking about the architecture, but sure.

> 
> > So this needs to:
> > - explicitly only apply to exceptions from AArch64
> > - handle exception from EL2, since this helper already deals with that
> 
> > The latter point of course means introducing GCSCR_EL2 (and everything
> > that depends on it, such as the trap handling).
> 
> For clarity, which trap handling specifically?

All the traps described in the GCSCR_EL2 documentation -- I see two
control bits described in K.a, all of which needs to be propagated and
their effects handled. Similarly, GCSPR_EL2 needs to be defined.

	M.

-- 
Without deviation from the norm, progress is not possible.