linux-kernel - Re: [PATCH v1 10/24] kvm: arm64: Extract parts of el2

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Date:   Mon, 16 Nov 2020 17:56:36 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Quentin Perret <qperret@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        Andrew Walbran <qwandor@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH v1 10/24] kvm: arm64: Extract parts of el2_setup into a
 macro

Hi Marc,

> > +	 * Check for VHE being present. x2 being non-zero indicates that we
> > +	 * do have VHE, and that the kernel is intended to run at EL2.
> >  	 */
> >  	mrs	x2, id_aa64mmfr1_el1
> >  	ubfx	x2, x2, #ID_AA64MMFR1_VHE_SHIFT, #4
> > -#else
> > -	mov	x2, xzr
> > -#endif
> > +	cbz	x2, el2_setup_nvhe
> 
> What initialises x2 to zero when CONFIG_VHE is disabled?

There is no need for x2 anymore, the nVHE code just falls through. Basically:

	el2_setup:
		< check CurrentEL >
		b.eq	1f
		ret
	1:
	#ifdef CONFIG_VHE
		< check has VHE >
		cbz	el2_setup_nvhe
		< VHE setup >
		ret
	#endif
	el2_setup_nvhe:
		< nVHE setup >
		eret

-David