[PATCH v7 13/16] arm64: head.S: el2_setup() to accept sctlr_el1 as an argument

[Catalin Marinas]

On Fri, Apr 01, 2016 at 05:53:37PM +0100, James Morse wrote:
> el2_setup() doesn't just configure el2, it configures el1 too. This
> means we can't use it to re-configure el2 after resume from hibernate,
> as we will be returned to el1 with the MMU turned off.
> 
> Split the sctlr_el1 setting code up, so that el2_setup() accepts an
> initial value as an argument. This value will be ignored if el2_setup()
> is called at el1: the running value will be preserved with endian
> correction.
> 
> Hibernate can now call el2_setup() to re-configure el2, passing the
> current sctlr_el1 as an argument.

I don't fully understand the description. The first paragraph says we
can't use el2_setup to re-configure el2 after resume from hibernate
while the last paragraph says that we can.

> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index a04fd7a9c102..627d66efec68 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -311,6 +311,16 @@ lr	.req	x30		// link register
>  	.endm
>  
>  /*
> + * Generate the initial sctlr_el1 value for el2_setup to set if we boot at EL2.
> + */
> +	.macro init_sctlr_el1 reg
> +		mov	\reg, #0x0800		// Set/clear RES{1,0} bits
> +CPU_BE(		movk	\reg, #0x33d0, lsl #16)	// Set EE and E0E on BE systems
> +CPU_LE(		movk	\reg, #0x30d0, lsl #16)	// Clear EE and E0E on LE systems
> +	.endm

I can see, at least in this patch, that all places where this macro is
invoked are immediately followed by a call to el2_setup. Can we not just
place this at the beginning of el2_setup?

> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 1217262b5210..097986152203 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -208,6 +208,7 @@ section_table:
>  
>  ENTRY(stext)
>  	bl	preserve_boot_args
> +	init_sctlr_el1	x0
>  	bl	el2_setup			// Drop to EL1, w20=cpu_boot_mode
>  	mov	x23, xzr			// KASLR offset, defaults to 0
>  	adrp	x24, __PHYS_OFFSET
> @@ -514,8 +515,12 @@ ENTRY(kimage_vaddr)
>   *
>   * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in x20 if
>   * booted in EL1 or EL2 respectively.
> + *
> + * If booted in EL2, SCTLR_EL1 will be initialised with the value in x0
> + * (otherwise the existing value will be preserved, with endian correction).
>   */
>  ENTRY(el2_setup)
> +	mov	x1, x0				// preserve passed-in sctlr_el1
>  	mrs	x0, CurrentEL
>  	cmp	x0, #CurrentEL_EL2
>  	b.ne	1f
> @@ -524,7 +529,7 @@ CPU_BE(	orr	x0, x0, #(1 << 25)	)	// Set the EE bit for EL2
>  CPU_LE(	bic	x0, x0, #(1 << 25)	)	// Clear the EE bit for EL2
>  	msr	sctlr_el2, x0
>  	b	2f
> -1:	mrs	x0, sctlr_el1
> +1:	mrs	x0, sctlr_el1			// ignore passed-in sctlr_el1
>  CPU_BE(	orr	x0, x0, #(3 << 24)	)	// Set the EE and E0E bits for EL1
>  CPU_LE(	bic	x0, x0, #(3 << 24)	)	// Clear the EE and E0E bits for EL1
>  	msr	sctlr_el1, x0

BTW, I wonder whether we need this read-modify-write sequence at all
rather than always setting a pre-set sane value (as per the
init_sctlr_el1 macro). This way we can always do this at the beginning
of el2_setup independent of whether we run in EL1 or EL2.

> @@ -578,6 +583,10 @@ set_hcr:
>  
>  3:
>  #endif
> +	/* use sctlr_el1 value we were provided with */
> +CPU_BE(	orr	x1, x1, #(3 << 24)	)	// Set the EE and E0E bits for EL1
> +CPU_LE(	bic	x1, x1, #(3 << 24)	)	// Clear the EE and E0E bits for EL1
> +	msr	sctlr_el1, x1

I don't think we need this here, the value passed already has the EE/E0E
bits set accordingly by the init_sctlr_el1 macro.

-- 
Catalin