linux-kernel - Re: [PATCH v15 4/6] KVM: arm64: Set PSTATE.EXLOCK when entering an exception

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Message-ID: <86segwdbv2.wl-maz@kernel.org>
Date: Mon, 08 Sep 2025 19:42:57 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 4/6] KVM: arm64: Set PSTATE.EXLOCK when entering an exception

On Thu, 21 Aug 2025 21:44:21 +0100,
Mark Brown <broonie@...nel.org> wrote:
> 
> On Wed, Aug 20, 2025 at 11:02:11PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@...nel.org> wrote:
> 
> > > +	// 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.

nit: I think you can drop the section number in the ARM ARM. The rule
"numbers" are stable across revision of the document, and K.a is
already absolutely ancient (over a year old and two revisions behind).

> > > +	new |= enter_exception64_gcs(vcpu, mode, target_mode);
> > > +
> > >  	new |= PSR_D_BIT;
> > >  	new |= PSR_A_BIT;
> > >  	new |= PSR_I_BIT;
> 
> > But that's not the only case where we have to deal with EXLOCK, is it?
> > What of ERET and its PAuth variants? R_TYTWB says:
> 
> > <quote>
> > If in AArch64 state, any of the following situations can cause an
> > illegal exception return:
> > 
> > [...]
> > 
> > - If the Effective value of GCSCR_ELx.EXLOCKEN is 1 and PSTATE.EXLOCK
> >   is 0, the execution of an exception return instruction to return to
> >   the current Exception level ELx.
> > </quote>
> 
> > My reading of the spec is that this needs handling.
> 
> Am I right in thinking that this handling is needed for the NV case
> only?

So far, NV is indeed the only case where we have to emulate ERET.

	M.

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