[PATCH 3/4] arm64: fix hyp mode mismatch detection

[Ard Biesheuvel]

On 13 March 2015 at 17:14, Mark Rutland <mark.rutland at arm.com> wrote:
> Commit 828e9834e9a5b7e6 ("arm64: head: create a new function for setting
> the boot_cpu_mode flag") added BOOT_CPU_MODE_EL1, a nonzero value
> replacing uses of zero. However it failed to update __boot_cpu_mode
> appropriately.
>
> A CPU booted at EL2 writes BOOT_CPU_MODE_EL2 to __boot_cpu_mode[0], and
> a CPU booted at EL1 writes BOOT_CPU_MODE_EL1 to __boot_cpu_mode[1].
> Later is_hyp_mode_mismatched() determines there to be a mismatch if
> __boot_cpu_mode[0] != __boot_cpu_mode[1].
>
> If all CPUs are booted at EL1, __boot_cpu_mode[0] will be set to
> BOOT_CPU_MODE_EL1, but __boot_cpu_mode[1] will retain its initial value
> of zero, and is_hyp_mode_mismatched will erroneously determine that the
> boot modes are mismatched. This hasn't been a problem so far, but later
> patches which will make use of is_hyp_mode_mismatched() expect it to
> work correctly.
>
> This patch initialises __boot_cpu_mode[1] to BOOT_CPU_MODE_EL1, fixing
> the erroneous mismatch detection when all CPUs are booted at EL1.
>

Maybe it's just me, but isn't it *much* easier to understand to
initialise both values to 0, and use 'both are non-zero' as the error
condition?
'HYP mode available' would then be '__boot_cpu_mode[0] ==
BOOT_CPU_MODE_EL2 && __boot_cpu_mode[1] == 0'


> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Marc Zyngier <marc.zyngier at arm.com>
> Cc: Will Deacon <will.deacon at arm.com>
> ---
>  arch/arm64/kernel/head.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 07f9305..d17649d 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -588,7 +588,7 @@ ENDPROC(set_cpu_boot_mode_flag)
>         .align  L1_CACHE_SHIFT
>  ENTRY(__boot_cpu_mode)
>         .long   BOOT_CPU_MODE_EL2
> -       .long   0
> +       .long   BOOT_CPU_MODE_EL1
>         .popsection
>
>  #ifdef CONFIG_SMP
> --
> 1.9.1
>