Subject: Re: [PATCH] powerpc: Fix booting P9 hash with CONFIG_PPC_RADIX_MMU=N

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 24 May 2017 14:26:38 +0530

Michael Neuling <[email-masked]> writes:

> Currently if you disable CONFIG_PPC_RADIX_MMU you'll crash on boot on
> a P9. This is because we still set MMU_FTR_TYPE_RADIX via
> ibm,pa-features and MMU_FTR_TYPE_RADIX is what's used for code patching
> in much of the asm code (ie. slb_miss_realmode)
>
> This patch fixes the problem by stopping MMU_FTR_TYPE_RADIX from being
> set from ibm.pa-features.
>
> We may eventually end up removing the CONFIG_PPC_RADIX_MMU option
> completely but until then this fixes the issue.
>
> Signed-off-by: Michael Neuling <[email-masked]>
> ---
>  arch/powerpc/kernel/prom.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 40c4887c27..f830562974 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -161,7 +161,9 @@ static struct ibm_pa_feature {
>  	{ .pabyte = 0,  .pabit = 3, .cpu_features  = CPU_FTR_CTRL },
>  	{ .pabyte = 0,  .pabit = 6, .cpu_features  = CPU_FTR_NOEXECUTE },
>  	{ .pabyte = 1,  .pabit = 2, .mmu_features  = MMU_FTR_CI_LARGE_PAGE },
> +#ifdef CONFIG_PPC_RADIX_MMU
>  	{ .pabyte = 40, .pabit = 0, .mmu_features  = MMU_FTR_TYPE_RADIX },
> +#endif
>  	{ .pabyte = 1,  .pabit = 1, .invert = 1, .cpu_features = CPU_FTR_NODSISRALIGN },
>  	{ .pabyte = 5,  .pabit = 0, .cpu_features  = CPU_FTR_REAL_LE,
>  				    .cpu_user_ftrs = PPC_FEATURE_TRUE_LE },
> -- 
> 2.11.0

Instead can we do that feature removal in mmu_early_init_devtree. ie, something like

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 8f6f2a173e47..8f43f3827bac 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -394,7 +394,7 @@ void __init mmu_early_init_devtree(void)
 {
 	/* Disable radix mode based on kernel command line. */
 	/* We don't yet have the machinery to do radix as a guest. */
-	if (disable_radix || !(mfmsr() & MSR_HV))
+	if (!IS_ENABLED(CONFIG_PPC_RADIX_MMU) || disable_radix || !(mfmsr() & MSR_HV))
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 
 	/*