linux-kernel - Re: [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2 mode

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Message-ID: <56A77D0B.50002@arm.com>
Date:	Tue, 26 Jan 2016 14:04:59 +0000
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2
 mode

On 25/01/16 15:53, Marc Zyngier wrote:
> With ARMv8.1 VHE, the architecture is able to (almost) transparently
> run the kernel at EL2, despite being written for EL1.
>
> This patch takes care of the "almost" part, mostly preventing the kernel
> from dropping from EL2 to EL1, and setting up the HYP configuration.

>   #ifdef CONFIG_COMPAT
> @@ -521,6 +542,15 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
>   	/* Stage-2 translation */
>   	msr	vttbr_el2, xzr
>
> +	cbz	x2, install_el2_stub

Though it is apparent, may be its worth adding a comment here that we don't drop to EL1 here ?

> +
> +	setup_vtcr x4, x5
> +
> +	mov	w20, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2
> +	isb
> +	ret

> +
> +install_el2_stub:

And a comment here mentioning, install the hyp stub and drops to EL1 ?

>   	/* Hypervisor stub */
>   	adrp	x0, __hyp_stub_vectors
>   	add	x0, x0, #:lo12:__hyp_stub_vectors
>

Cheers
Suzuki