Re: [PATCH] powerpc/powernv: Fix boot on Power8 bare metal due to opal_configure_cores()

[Balbir Singh <bsingharora@gmail.com>]

On Mon, 2017-07-17 at 21:31 +1000, Michael Ellerman wrote:
> In commit 1c0eaf0f56d6 ("powerpc/powernv: Tell OPAL about our MMU mode
> on POWER9"), we added additional flags to the OPAL call to configure
> CPUs at boot.
> 
> These flags only work on Power9 firmwares, and worse can cause boot
> failures on Power8 machines, so we check for CPU_FTR_ARCH_300 (aka POWER9)
> before adding the extra flags.
> 
> Unfortunately we forgot that opal_configure_cores() is called before
> the CPU feature checks are dynamically patched, meaning the check
> always returns true.
> 
> We definitely need to do something to make the CPU feature checks less
> prone to bugs like this, but for now the minimal fix is to use
> early_cpu_has_feature().
> 
> Reported-and-tested-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
> Fixes: 1c0eaf0f56d6 ("powerpc/powernv: Tell OPAL about our MMU mode on POWER9")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/platforms/powernv/opal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
> index 9b87abb178f0..cad6b57ce494 100644
> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -78,7 +78,7 @@ void opal_configure_cores(void)
>  	 *  ie. Host hash  supports  hash guests
>  	 *      Host radix supports  hash/radix guests
>  	 */
> -	if (cpu_has_feature(CPU_FTR_ARCH_300)) {
> +	if (early_cpu_has_feature(CPU_FTR_ARCH_300)) {
>  		reinit_flags |= OPAL_REINIT_CPUS_MMU_HASH;
>  		if (early_radix_enabled())
>  			reinit_flags |= OPAL_REINIT_CPUS_MMU_RADIX;

We do have CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG, but I am not sure if there
is an efficient way to enable it till we actually get the key enabled. I wonder
if a branch hint will help, but I still feel its expensive.

Acked-by: Balbir Singh <bsingharora@gmail.com>