Re: [PATCH 10/13] arm64: Add support for running Linux in EL2 mode

[Will Deacon <will.deacon@arm.com>]

On Wed, Jul 08, 2015 at 05:19:13PM +0100, Marc Zyngier wrote:
> With the 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.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/kernel/head.S | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index c0ff3ce..a179747 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -29,6 +29,7 @@
>  #include <asm/asm-offsets.h>
>  #include <asm/cache.h>
>  #include <asm/cputype.h>
> +#include <asm/kvm_mmu.h>
>  #include <asm/memory.h>
>  #include <asm/thread_info.h>
>  #include <asm/pgtable-hwdef.h>
> @@ -481,8 +482,16 @@ CPU_LE(	bic	x0, x0, #(3 << 24)	)	// Clear the EE and E0E bits for EL1
>  	isb
>  	ret
>  
> +	/* Check for VHE being present */
> +2:	mrs	x2, id_aa64mmfr1_el1
> +	ubfx	x2, x2, #8, #4
> +
>  	/* Hyp configuration. */
> -2:	mov	x0, #(1 << 31)			// 64-bit EL1
> +	mov	x0, #HCR_RW			// 64-bit EL1
> +	cbz	x2, set_hcr
> +	orr	x0, x0, #HCR_TGE		// Enable Host Extensions
> +	orr	x0, x0, #HCR_E2H
> +set_hcr:
>  	msr	hcr_el2, x0
>  
>  	/* Generic timers. */
> @@ -522,6 +531,9 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
>  
>  	/* Coprocessor traps. */
>  	mov	x0, #0x33ff

These bits are RES0 with VHE enabled, afaict.

> +	cbz	x2, set_cptr
> +	orr	x0, x0, #(3 << 20)		// Don't trap FP
> +set_cptr:
>  	msr	cptr_el2, x0			// Disable copro. traps to EL2
>  
>  #ifdef CONFIG_COMPAT
> @@ -531,6 +543,15 @@ 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
> +
> +	setup_vtcr x4, x5
> +
> +	mov	w20, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2

You do this in install_el2_stub as well -- can you move it above the cbz?

Will