[U-Boot] [PATCH v4 2/9] efi_loader: AArch64: Run EFI payloads in EL2 if U-Boot runs in EL3

[york sun]

On 06/20/2016 04:07 PM, Alexander Graf wrote:
> Some boards decided not to run ATF or other secure firmware in EL3, so
> they instead run U-Boot there. The uEFI spec doesn't know what EL3 is
> though - it only knows about EL2 and EL1. So if we see that we're running
> in EL3, let's get into EL2 to make payloads happy.
>
> Signed-off-by: Alexander Graf <agraf at suse.de>
> ---
>   arch/arm/include/asm/armv8/mmu.h | 19 ++++++++++++-------
>   cmd/bootefi.c                    | 11 +++++++++++
>   2 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/include/asm/armv8/mmu.h b/arch/arm/include/asm/armv8/mmu.h
> index 0d08ed3..876a2b2 100644
> --- a/arch/arm/include/asm/armv8/mmu.h
> +++ b/arch/arm/include/asm/armv8/mmu.h
> @@ -116,19 +116,24 @@
>   static inline void set_ttbr_tcr_mair(int el, u64 table, u64 tcr, u64 attr)
>   {
>   	asm volatile("dsb sy");
> -	if (el == 1) {
> +	switch (el) {
> +	case 1:
>   		asm volatile("msr ttbr0_el1, %0" : : "r" (table) : "memory");
>   		asm volatile("msr tcr_el1, %0" : : "r" (tcr) : "memory");
>   		asm volatile("msr mair_el1, %0" : : "r" (attr) : "memory");
> -	} else if (el == 2) {
> -		asm volatile("msr ttbr0_el2, %0" : : "r" (table) : "memory");
> -		asm volatile("msr tcr_el2, %0" : : "r" (tcr) : "memory");
> -		asm volatile("msr mair_el2, %0" : : "r" (attr) : "memory");
> -	} else if (el == 3) {
> +		break;
> +	case 3:
>   		asm volatile("msr ttbr0_el3, %0" : : "r" (table) : "memory");
>   		asm volatile("msr tcr_el3, %0" : : "r" (tcr) : "memory");
>   		asm volatile("msr mair_el3, %0" : : "r" (attr) : "memory");
> -	} else {
> +
> +		/* We may switch to EL2 later, so set those too; fall through */
> +	case 2:
> +		asm volatile("msr ttbr0_el2, %0" : : "r" (table) : "memory");
> +		asm volatile("msr tcr_el2, %0" : : "r" (tcr) : "memory");
> +		asm volatile("msr mair_el2, %0" : : "r" (attr) : "memory");
> +		break;


This may be problematic. If we use secure memory for EL3, the MMU tables 
have to be within the secure memory. But EL2 will not be able to access 
it. I believe you have verified this patch set actually work. I am 
curious how it work.

York