[PATCH v5 5/7] powerpc/pseries: flush SLB contents on SLB MCE errors.

[Michael Ellerman]

Michal Suchánek <msuchanek at suse.de> writes:
> On Tue, 3 Jul 2018 08:08:14 +1000
> Nicholas Piggin <npiggin at gmail.com> wrote:
>> On Mon, 02 Jul 2018 11:17:06 +0530
>> Mahesh J Salgaonkar <mahesh at linux.vnet.ibm.com> wrote:
>> > From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>> > 
>> > On pseries, as of today system crashes if we get a machine check
>> > exceptions due to SLB errors. These are soft errors and can be
>> > fixed by flushing the SLBs so the kernel can continue to function
>> > instead of system crash. We do this in real mode before turning on
>> > MMU. Otherwise we would run into nested machine checks. This patch
>> > now fetches the rtas error log in real mode and flushes the SLBs on
>> > SLB errors.
>> > 
>> > Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>> > ---
>> >  arch/powerpc/include/asm/book3s/64/mmu-hash.h |    1 
>> >  arch/powerpc/include/asm/machdep.h            |    1 
>> >  arch/powerpc/kernel/exceptions-64s.S          |   42
>> > +++++++++++++++++++++ arch/powerpc/kernel/mce.c
>> > |   16 +++++++- arch/powerpc/mm/slb.c                         |
>> > 6 +++ arch/powerpc/platforms/powernv/opal.c         |    1 
>> >  arch/powerpc/platforms/pseries/pseries.h      |    1 
>> >  arch/powerpc/platforms/pseries/ras.c          |   51
>> > +++++++++++++++++++++++++
>> > arch/powerpc/platforms/pseries/setup.c        |    1 9 files
>> > changed, 116 insertions(+), 4 deletions(-) 
>> 
>> 
>> > +TRAMP_REAL_BEGIN(machine_check_pSeries_early)
>> > +BEGIN_FTR_SECTION
>> > +	EXCEPTION_PROLOG_1(PACA_EXMC, NOTEST, 0x200)
>> > +	mr	r10,r1			/* Save r1 */
>> > +	ld	r1,PACAMCEMERGSP(r13)	/* Use MC emergency
>> > stack */
>> > +	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack
>> > frame		*/
>> > +	mfspr	r11,SPRN_SRR0		/* Save SRR0 */
>> > +	mfspr	r12,SPRN_SRR1		/* Save SRR1 */
>> > +	EXCEPTION_PROLOG_COMMON_1()
>> > +	EXCEPTION_PROLOG_COMMON_2(PACA_EXMC)
>> > +	EXCEPTION_PROLOG_COMMON_3(0x200)
>> > +	addi	r3,r1,STACK_FRAME_OVERHEAD
>> > +	BRANCH_LINK_TO_FAR(machine_check_early) /* Function call
>> > ABI */  
>> 
>> Is there any reason you can't use the existing
>> machine_check_powernv_early code to do all this?
>
> Code sharing is nice but if we envision this going to stable kernels
> butchering the existing handler is going to be a nightmare. The code is
> quite a bit different between kernel versions.

I'm not sure if we'll send it to stable kernels. But we obviously will
back port it to some distros :)

So if sharing the code is a significant impediment to that, then I'm
happy if we don't share code initially. That could be done as a
follow-up to this series.

cheers