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

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

[Nicholas Piggin]

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.

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

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

[Aneesh Kumar K.V]

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

Re: powerpc/64s/radix: Fix radix segment exception handling

[Michael Ellerman]

On Fri, 2019-03-29 at 07:42:57 UTC, Nicholas Piggin wrote:
> 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.
> 
> 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>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/7100e8704b61247649c50551b965e71d

cheers

Re: powerpc/64s/radix: Fix radix segment exception handling

[Nicholas Piggin]

Michael Ellerman's on April 11, 2019 12:49 am:
> On Fri, 2019-03-29 at 07:42:57 UTC, Nicholas Piggin wrote:
>> 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.
>> 
>> 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>
>> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> 
> Applied to powerpc fixes, thanks.
> 
> https://git.kernel.org/powerpc/c/7100e8704b61247649c50551b965e71d

I sent a v2 with a selftests that triggers the crash if you want it.
Code was unchanged to no big deal there.

Thanks,
Nick

Re: powerpc/64s/radix: Fix radix segment exception handling

[Michael Ellerman]

Nicholas Piggin <npiggin@gmail.com> writes:
> Michael Ellerman's on April 11, 2019 12:49 am:
>> On Fri, 2019-03-29 at 07:42:57 UTC, Nicholas Piggin wrote:
>>> 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.
>>> 
>>> 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>
>>> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> 
>> Applied to powerpc fixes, thanks.
>> 
>> https://git.kernel.org/powerpc/c/7100e8704b61247649c50551b965e71d
>
> I sent a v2 with a selftests that triggers the crash if you want it.
> Code was unchanged to no big deal there.

Yeah I checked the kernel part was unchanged so stuck with v1.

I also sent a self test, which is similar but slightly different to
yours, though yours is better in general. I'll try and merge them into
one test.

cheers

Re: powerpc/64s/radix: Fix radix segment exception handling

[Nicholas Piggin]

Michael Ellerman's on April 13, 2019 1:39 pm:
> Nicholas Piggin <npiggin@gmail.com> writes:
>> Michael Ellerman's on April 11, 2019 12:49 am:
>>> On Fri, 2019-03-29 at 07:42:57 UTC, Nicholas Piggin wrote:
>>>> 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.
>>>> 
>>>> 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>
>>>> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>> 
>>> Applied to powerpc fixes, thanks.
>>> 
>>> https://git.kernel.org/powerpc/c/7100e8704b61247649c50551b965e71d
>>
>> I sent a v2 with a selftests that triggers the crash if you want it.
>> Code was unchanged to no big deal there.
> 
> Yeah I checked the kernel part was unchanged so stuck with v1.
> 
> I also sent a self test, which is similar but slightly different to
> yours, though yours is better in general. I'll try and merge them into
> one test.

If you don't mind that would be good. The siglongjmp handler is
cleaner though, and should make it simpler to test ifetch accesses.
We just need to get the sig info into yours, and an array of
interesting addresses.

Thanks,
Nick