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

[Christoffer Dall <christoffer.dall@linaro.org>]

On Mon, Jan 25, 2016 at 03:53:54PM +0000, 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.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/Kconfig       | 13 +++++++++++++
>  arch/arm64/kernel/head.S | 32 +++++++++++++++++++++++++++++++-
>  2 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 8cc6228..ada34df 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -750,6 +750,19 @@ config ARM64_LSE_ATOMICS
>  	  not support these instructions and requires the kernel to be
>  	  built with binutils >= 2.25.
>  
> +config ARM64_VHE
> +	bool "Enable support for Virtualization Host Extension (VHE)"

Extensions (plural)

> +	default y
> +	help
> +	  Virtualization Host Extension (VHE) allows the kernel to run

same

> +	  directly at EL2 (instead of EL1) on processors that support
> +	  it. This leads to better performance for KVM, as it reduces

s/it/them/ then?

> +	  the cost of the world switch.
> +
> +	  Selecting this option allows the VHE feature to be detected
> +	  at runtime, and does not affect processors that do not
> +	  implement this feature.
> +
>  endmenu
>  
>  endmenu
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index ffe9c2b..2a7134c 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -30,6 +30,7 @@
>  #include <asm/cache.h>
>  #include <asm/cputype.h>
>  #include <asm/kernel-pgtable.h>
> +#include <asm/kvm_mmu.h>
>  #include <asm/memory.h>
>  #include <asm/pgtable-hwdef.h>
>  #include <asm/pgtable.h>
> @@ -464,8 +465,25 @@ CPU_LE(	bic	x0, x0, #(3 << 24)	)	// Clear the EE and E0E bits for EL1
>  	isb
>  	ret
>  
> +2:
> +#ifdef CONFIG_ARM64_VHE
> +	/*
> +	 * Check for VHE being present. For the rest of the EL2 setup,
> +	 * 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, #8, #4
> +#else
> +	mov	x2, xzr
> +#endif
> +
>  	/* 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. */
> @@ -507,6 +525,9 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
>  
>  	/* Coprocessor traps. */
>  	mov	x0, #0x33ff
> +	cbz	x2, set_cptr
> +	orr	x0, x0, #(3 << 20)		// Don't trap FP

nit: If you make that define we discussed earlier you can use it here too

> +set_cptr:
>  	msr	cptr_el2, x0			// Disable copro. traps to EL2
>  
>  #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
> +
> +	setup_vtcr x4, x5
> +
> +	mov	w20, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2
> +	isb
> +	ret
> +
> +install_el2_stub:
>  	/* Hypervisor stub */
>  	adrp	x0, __hyp_stub_vectors
>  	add	x0, x0, #:lo12:__hyp_stub_vectors
> -- 
> 2.1.4
> 

Otherwise:

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>