Re: [PATCH] powerpc/64s/radix: Fix radix segment exception handling

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

Nicholas Piggin <npiggin@gmail.com> writes:

> Commit 48e7b76957 ("powerpc/64s/hash: Convert SLB miss handlers to C")
> broke the radix-mode segment exception handler. In radix mode, this is
> exception is not an SLB miss, rather it signals that the EA is outside
> the range translated by any page table.
>
> The commit lost the radix feature alternate code patch, which can
> cause faults to some EAs to kernel BUG at arch/powerpc/mm/slb.c:639!
>
> The original radix code would send faults to slb_miss_large_addr,
> which would end up faulting due to slb_addr_limit being 0. This patch
> sends radix directly to do_bad_slb_fault, which is a bit clearer.
>

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

> Fixes: 48e7b76957 ("powerpc/64s/hash: Convert SLB miss handlers to C")
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Reported-by: Anton Blanchard <anton@samba.org>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/exceptions-64s.S | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index a5b8fbae56a0..9481a117e242 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -656,11 +656,17 @@ EXC_COMMON_BEGIN(data_access_slb_common)
>  	ld	r4,PACA_EXSLB+EX_DAR(r13)
>  	std	r4,_DAR(r1)
>  	addi	r3,r1,STACK_FRAME_OVERHEAD
> +BEGIN_MMU_FTR_SECTION
> +	/* HPT case, do SLB fault */
>  	bl	do_slb_fault
>  	cmpdi	r3,0
>  	bne-	1f
>  	b	fast_exception_return
>  1:	/* Error case */
> +MMU_FTR_SECTION_ELSE
> +	/* Radix case, access is outside page table range */
> +	li	r3,-EFAULT
> +ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
>  	std	r3,RESULT(r1)
>  	bl	save_nvgprs
>  	RECONCILE_IRQ_STATE(r10, r11)
> @@ -705,11 +711,17 @@ EXC_COMMON_BEGIN(instruction_access_slb_common)
>  	EXCEPTION_PROLOG_COMMON(0x480, PACA_EXSLB)
>  	ld	r4,_NIP(r1)
>  	addi	r3,r1,STACK_FRAME_OVERHEAD
> +BEGIN_MMU_FTR_SECTION
> +	/* HPT case, do SLB fault */
>  	bl	do_slb_fault
>  	cmpdi	r3,0
>  	bne-	1f
>  	b	fast_exception_return
>  1:	/* Error case */
> +MMU_FTR_SECTION_ELSE
> +	/* Radix case, access is outside page table range */
> +	li	r3,-EFAULT
> +ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
>  	std	r3,RESULT(r1)
>  	bl	save_nvgprs
>  	RECONCILE_IRQ_STATE(r10, r11)
> -- 
> 2.20.1