Re: [PATCH v2] powerpc/interrupt: Use early_radix_enabled() in NMI real-mode guard

[Shrikanth Hegde <sshegde@linux.ibm.com>]

On 9/9/26 2:42 PM, Venkat Rao Bagalkote wrote:
> radix_enabled() uses a jump label which is only valid after
> mmu_feature_keys_init() is called. Before that point, on a pSeries
> hash guest, early_check_vec5() clears MMU_FTR_TYPE_RADIX in
> cur_cpu_spec->mmu_features but the jump label has not yet been patched,
> so radix_enabled() incorrectly returns true.
> 

The usage window where it goes wrong is:

early_setup:
	configure_exceptions();
	<exception can happen now, and could prepare/exit of corresponding exception>
		<those could use radix_enabled() >
	setup_feature_keys();
	<jump labels are setup and post this it is safe to use radix_enabled()>

But since common wrappers don't have the context of early or late,
using early_radix_enabled() is safer option.

Commit message could convey the same.

> Replace radix_enabled() with early_radix_enabled() which does a plain
> bitmask check against cur_cpu_spec->mmu_features and is correct at all
> times, including before jump label initialization.
> 

If you have data, please put the values of both early_radix_enabled and radix_enabled()
in hash/radix guests in the chaneglog to ensure replacing with early variant
is functionally safe.

> Add the missing #include <asm/mmu.h> since early_radix_enabled() is
> declared there.
> 
> Fixes: 8d0e21012743 ("powerpc/mce: Avoid nmi_enter/exit in real mode on pseries hash")
> Signed-off-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Reviewed-by: Mukesh Kumar Chaurasiya <mkchauras@gmail.com>
> ---
> v2:
>   - Added Fixes: tag referencing commit 8d0e21012743.
>   - Included <asm/mmu.h> in alphabetical order.
>   - Added Reviewed-by tag from Mukesh.
> 
>   arch/powerpc/include/asm/interrupt.h | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> index 1b45a49e9bed..355f6bbf9894 100644
> --- a/arch/powerpc/include/asm/interrupt.h
> +++ b/arch/powerpc/include/asm/interrupt.h
> @@ -70,6 +70,7 @@
>   #include <linux/irq-entry-common.h>
>   
>   #include <asm/kprobes.h>
> +#include <asm/mmu.h>
>   #include <asm/runlatch.h>
>   
>   #ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
> @@ -290,7 +291,7 @@ interrupt_handler long func(struct pt_regs *regs)			\
>   		state = irqentry_nmi_enter(regs);			\
>   	} else if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) &&			\
>   		   firmware_has_feature(FW_FEATURE_LPAR) &&		\
> -		   !radix_enabled()) {					\
> +		   !early_radix_enabled()) {				\
>   		/* no nmi_entry for a pseries hash guest		\
>   		 * taking a real mode exception */			\
>   	} else if (IS_ENABLED(CONFIG_KASAN)) {				\
> @@ -307,7 +308,7 @@ interrupt_handler long func(struct pt_regs *regs)			\
>   		irqentry_nmi_exit(regs, state);				\
>   	} else if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) &&			\
>   		   firmware_has_feature(FW_FEATURE_LPAR) &&		\
> -		   !radix_enabled()) {					\
> +		   !early_radix_enabled()) {				\
>   		/* no nmi_exit for a pseries hash guest			\
>   		 * taking a real mode exception */			\
>   	} else if (IS_ENABLED(CONFIG_KASAN)) {				\