Re: [kvm-unit-tests PATCH 5/6] arm64: Configure SCTLR_EL1 at boot

[Andre Przywara <andre.przywara@arm.com>]

On Sat, 27 Feb 2021 10:42:00 +0000
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

Hi,

> Some fields in SCTLR_EL1 are UNKNOWN at reset and the arm64 boot
> requirements, as stated by Linux in Documentation/arm64/booting.rst, do not
> specify a particular value for all the fields. Do not rely on the good will
> of the hypervisor and userspace to set SCTLR_EL1 to a sane value (by their
> definition of sane) and set SCTLR_EL1 explicitely before running setup().
> This will ensure that all tests are performed with the hardware set up
> identically, regardless of the KVM or VMM versions.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>

Can confirm that the RES1 bits match the ARM ARM, and that it's indeed
a good idea to start from a known good state:

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre

> ---
>  lib/arm64/asm/sysreg.h | 7 +++++++
>  arm/cstart64.S         | 5 +++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/lib/arm64/asm/sysreg.h b/lib/arm64/asm/sysreg.h
> index 9d6b4fc66936..18c4ed39557a 100644
> --- a/lib/arm64/asm/sysreg.h
> +++ b/lib/arm64/asm/sysreg.h
> @@ -8,6 +8,8 @@
>  #ifndef _ASMARM64_SYSREG_H_
>  #define _ASMARM64_SYSREG_H_
>  
> +#include <linux/const.h>
> +
>  #define sys_reg(op0, op1, crn, crm, op2) \
>  	((((op0)&3)<<19)|((op1)<<16)|((crn)<<12)|((crm)<<8)|((op2)<<5))
>  
> @@ -87,4 +89,9 @@ asm(
>  #define SCTLR_EL1_A	(1 << 1)
>  #define SCTLR_EL1_M	(1 << 0)
>  
> +#define SCTLR_EL1_RES1	(_BITUL(7) | _BITUL(8) | _BITUL(11) | _BITUL(20) | \
> +			 _BITUL(22) | _BITUL(23) | _BITUL(28) | _BITUL(29))
> +#define INIT_SCTLR_EL1_MMU_OFF	\
> +			SCTLR_EL1_RES1
> +
>  #endif /* _ASMARM64_SYSREG_H_ */
> diff --git a/arm/cstart64.S b/arm/cstart64.S
> index f6c5d2ebccf3..42a838ff4c38 100644
> --- a/arm/cstart64.S
> +++ b/arm/cstart64.S
> @@ -52,6 +52,11 @@ start:
>  	b	1b
>  
>  1:
> +	/* set SCTLR_EL1 to a known value */
> +	ldr	x4, =INIT_SCTLR_EL1_MMU_OFF
> +	msr	sctlr_el1, x4
> +	isb
> +
>  	/* set up stack */
>  	mov	x4, #1
>  	msr	spsel, x4