Re: [PATCH v3 05/17] arm64: Don't enable VHE for the kernel if OVERRIDE_HVHE is set

From: Oliver Upton <oliver.upton@linux.dev>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>,
	kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Quentin Perret <qperret@google.com>,
	Will Deacon <will@kernel.org>, Fuad Tabba <tabba@google.com>
Subject: Re: [PATCH v3 05/17] arm64: Don't enable VHE for the kernel if OVERRIDE_HVHE is set
Date: Mon, 12 Jun 2023 21:20:26 +0200	[thread overview]
Message-ID: <ZIdv+q9hemnlIDtl@linux.dev> (raw)
In-Reply-To: <ZIduFSAPFumGotwV@arm.com>

Hey Catalin,

Thanks a bunch for the reviews/acks, I plan on queueing this up for 6.5.

On Mon, Jun 12, 2023 at 08:12:21PM +0100, Catalin Marinas wrote:
> On Fri, Jun 09, 2023 at 05:21:48PM +0100, Marc Zyngier wrote:
> > If the OVERRIDE_HVHE SW override is set (as a precursor of
> > the KVM_HVHE capability), do not enable VHE for the kernel
> > and drop to EL1 as if VHE was either disabled or unavailable.
> > 
> > Further changes will enable VHE at EL2 only, with the kernel
> > still running at EL1.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kernel/hyp-stub.S | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> > index 9439240c3fcf..5c71e1019545 100644
> > --- a/arch/arm64/kernel/hyp-stub.S
> > +++ b/arch/arm64/kernel/hyp-stub.S
> > @@ -82,7 +82,15 @@ SYM_CODE_START_LOCAL(__finalise_el2)
> >  	tbnz	x1, #0, 1f
> >  
> >  	// Needs to be VHE capable, obviously
> > -	check_override id_aa64mmfr1 ID_AA64MMFR1_EL1_VH_SHIFT 2f 1f x1 x2
> > +	check_override id_aa64mmfr1 ID_AA64MMFR1_EL1_VH_SHIFT 0f 1f x1 x2
> > +
> > +0:	// Check whether we only want the hypervisor to run VHE, not the kernel
> > +	adr_l	x1, arm64_sw_feature_override
> > +	ldr	x2, [x1, FTR_OVR_VAL_OFFSET]
> > +	ldr	x1, [x1, FTR_OVR_MASK_OFFSET]
> > +	and	x2, x2, x1
> > +	ubfx	x2, x2, #ARM64_SW_FEATURE_OVERRIDE_HVHE, #4
> > +	cbz	x2, 2f
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> 
> (I think we are trying too hard to make this look like a hardware
> features when a tbz would do ;)).

I had a similar feeling and whined on v1 :) Perhaps we can make a macro
for testing software feature if/when we ever stop representing SW
features like ID registers, per your suggestion.

--
Thanks,
Oliver

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