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

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Message-ID: <ZwFJvV7lrFStWD-r@finisterre.sirena.org.uk>
Date: Sat, 5 Oct 2024 15:14:21 +0100
From: Mark Brown <broonie@...nel.org>
To: Marc Zyngier <maz@...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 v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an
 exception

On Sat, Oct 05, 2024 at 01:36:09PM +0100, Marc Zyngier wrote:
> Mark Brown <broonie@...nel.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.

> 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?

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