Re: [PATCH] powerpc: Fix faults caused by radix patching of SLB miss handler

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Michael Ellerman <mpe@ellerman.id.au> writes:

> As part of the Radix MMU support we added some feature sections in the
> SLB miss handler. These are intended to catch the case that we
> incorrectly take an SLB miss when Radix is enabled, and instead of
> crashing weirdly they bail out to a well defined exit path and trigger
> an oops.
>
> However the way they were written meant the bailout case was enabled by
> default until we did CPU feature patching.
>
> On powermacs the early debug prints in setup_system() can cause an SLB
> miss, which happens before code patching, and so the SLB miss handler
> would incorrectly bailout and crash during boot.
>
> Fix it by inverting the sense of the feature section, so that the code
> which is in place at boot is correct for the hash case. Once we
> determine we are using Radix - which will never happen on a powermac -
> only then do we patch in the bailout case which unconditionally jumps.
>
> Fixes: caca285e5ab4 ("powerpc/mm/radix: Use STD_MMU_64 to properly isolate hash related code")
> Reported-by: Denis Kirjanov <kda@linux-powerpc.org>
> Tested-by: Denis Kirjanov <kda@linux-powerpc.org>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>


Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>  arch/powerpc/kernel/exceptions-64s.S | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 4c9440629128..8bcc1b457115 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -1399,11 +1399,12 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_RADIX)
>  	lwz	r9,PACA_EXSLB+EX_CCR(r13)	/* get saved CR */
>
>  	mtlr	r10
> -BEGIN_MMU_FTR_SECTION
> -	b	2f
> -END_MMU_FTR_SECTION_IFSET(MMU_FTR_RADIX)
>  	andi.	r10,r12,MSR_RI	/* check for unrecoverable exception */
> +BEGIN_MMU_FTR_SECTION
>  	beq-	2f
> +FTR_SECTION_ELSE
> +	b	2f
> +ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_RADIX)
>
>  .machine	push
>  .machine	"power4"
> -- 
> 2.5.0