Re: [PATCH v2 2/2] KVM: arm64: Trap access to SMPRI_EL1 and TPIDR2 in VHE mode

[Mark Brown <broonie@kernel.org>]

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On Tue, Nov 01, 2022 at 01:33:16PM +0000, Marc Zyngier wrote:
> Mark Brown <broonie@kernel.org> wrote:

> > -	if (cpus_have_final_cap(ARM64_SME))
> > +	if (cpus_have_final_cap(ARM64_SME)) {
> >  		write_sysreg(read_sysreg(sctlr_el2) & ~SCTLR_ELx_ENTP2,
> >  			     sctlr_el2);

> I still question this. As far as I can tell, it only affects the host
> context (HCR_EL2.{E2H,TGE}={1,1}).

> This is outlined in the description of the HFGWTR_EL2.nTPIDR2_EL0 bit:

Oh, I see what you meant there - I was purely focusing on the new code
with the fine grained traps, not the existing code.

> So I can only conclude that messing with SCTLR_EL2 is superfluous and
> doesn't affect the execution in a guest context.

Yes, if you look at the pseudocode for TPIDR2_EL0 that's the case.  It's
either EnTP2 for HCR_EL2.<E2H,TGE> == '11' or the fine grained trap
otherwise.

> > +		/*
> > +		 * Enable access to SMPRI_EL1 - we don't need to
> > +		 * control nTPIDR2_EL0 in VHE mode.
> > +		 */

> This comment is factually wrong.

Bah, I fixed one but not the other sorry :/

> Date: Tue, 1 Nov 2022 12:19:51 +0000
> Subject: [PATCH] KVM: arm64: Fix SMPRI_EL1/TPIDR2_EL0 trapping on VHE
> 
> The trapping of SMPRI_EL1 and TPIDR2_EL0 currently only really
> work on nVHE, as only this mode uses the fine-grained trapping
> that controls these two registers.
> 
> Move the trapping enable/disable code into
> __{de,}activate_traps_common(), allowing it to be called when it
> actually matters on VHE, and remove the flipping of EL2 control
> for TPIDR2_EL0, which only affects the host access of this
> register.
> 
> Fixes: 861262ab8627 ("KVM: arm64: Handle SME host state when running guests")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org

Reported-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>

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