Re: [PATCH v6 5/8] powerpc/pseries: flush SLB contents on SLB MCE errors.

[Nicholas Piggin <npiggin@gmail.com>]

On Wed, 04 Jul 2018 23:28:21 +0530
Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:

> From: Mahesh Salgaonkar <mahesh@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@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/pseries/pseries.h      |    1 
>  arch/powerpc/platforms/pseries/ras.c          |   51 +++++++++++++++++++++++++
>  arch/powerpc/platforms/pseries/setup.c        |    1 
>  8 files changed, 116 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu-hash.h b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
> index 50ed64fba4ae..cc00a7088cf3 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu-hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
> @@ -487,6 +487,7 @@ extern void hpte_init_native(void);
>  
>  extern void slb_initialize(void);
>  extern void slb_flush_and_rebolt(void);
> +extern void slb_flush_and_rebolt_realmode(void);
>  
>  extern void slb_vmalloc_update(void);
>  extern void slb_set_size(u16 size);
> diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
> index ffe7c71e1132..fe447e0d4140 100644
> --- a/arch/powerpc/include/asm/machdep.h
> +++ b/arch/powerpc/include/asm/machdep.h
> @@ -108,6 +108,7 @@ struct machdep_calls {
>  
>  	/* Early exception handlers called in realmode */
>  	int		(*hmi_exception_early)(struct pt_regs *regs);
> +	int		(*machine_check_early)(struct pt_regs *regs);
>  
>  	/* Called during machine check exception to retrive fixup address. */
>  	bool		(*mce_check_early_recovery)(struct pt_regs *regs);
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index f283958129f2..0038596b7906 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -332,6 +332,9 @@ TRAMP_REAL_BEGIN(machine_check_pSeries)
>  machine_check_fwnmi:
>  	SET_SCRATCH0(r13)		/* save r13 */
>  	EXCEPTION_PROLOG_0(PACA_EXMC)
> +BEGIN_FTR_SECTION
> +	b	machine_check_pSeries_early
> +END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
>  machine_check_pSeries_0:
>  	EXCEPTION_PROLOG_1(PACA_EXMC, KVMTEST_PR, 0x200)
>  	/*
> @@ -343,6 +346,45 @@ machine_check_pSeries_0:
>  
>  TRAMP_KVM_SKIP(PACA_EXMC, 0x200)
>  
> +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 */
> +
> +	/* Move original SRR0 and SRR1 into the respective regs */
> +	ld	r9,_MSR(r1)
> +	mtspr	SPRN_SRR1,r9
> +	ld	r3,_NIP(r1)
> +	mtspr	SPRN_SRR0,r3
> +	ld	r9,_CTR(r1)
> +	mtctr	r9
> +	ld	r9,_XER(r1)
> +	mtxer	r9
> +	ld	r9,_LINK(r1)
> +	mtlr	r9
> +	REST_GPR(0, r1)
> +	REST_8GPRS(2, r1)
> +	REST_GPR(10, r1)
> +	ld	r11,_CCR(r1)
> +	mtcr	r11
> +	REST_GPR(11, r1)
> +	REST_2GPRS(12, r1)
> +	/* restore original r1. */
> +	ld	r1,GPR1(r1)
> +	SET_SCRATCH0(r13)		/* save r13 */
> +	EXCEPTION_PROLOG_0(PACA_EXMC)
> +	b	machine_check_pSeries_0
> +END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
> +
>  EXC_COMMON_BEGIN(machine_check_common)
>  	/*
>  	 * Machine check is different because we use a different
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index efdd16a79075..221271c96a57 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -488,9 +488,21 @@ long machine_check_early(struct pt_regs *regs)
>  {
>  	long handled = 0;
>  
> -	__this_cpu_inc(irq_stat.mce_exceptions);
> +	/*
> +	 * For pSeries we count mce when we go into virtual mode machine
> +	 * check handler. Hence skip it. Also, We can't access per cpu
> +	 * variables in real mode for LPAR.
> +	 */
> +	if (early_cpu_has_feature(CPU_FTR_HVMODE))
> +		__this_cpu_inc(irq_stat.mce_exceptions);
>  
> -	if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
> +	/*
> +	 * See if platform is capable of handling machine check.
> +	 * Otherwise fallthrough and allow CPU to handle this machine check.
> +	 */
> +	if (ppc_md.machine_check_early)
> +		handled = ppc_md.machine_check_early(regs);
> +	else if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
>  		handled = cur_cpu_spec->machine_check_early(regs);
>  	return handled;
>  }

This looks fine to me after Michal's patch. Not sure if you want to
fold them or add his immediately after this one in your series.

> diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
> index 66577cc66dc9..5b1813b98358 100644
> --- a/arch/powerpc/mm/slb.c
> +++ b/arch/powerpc/mm/slb.c
> @@ -145,6 +145,12 @@ void slb_flush_and_rebolt(void)
>  	get_paca()->slb_cache_ptr = 0;
>  }
>  
> +void slb_flush_and_rebolt_realmode(void)
> +{
> +	__slb_flush_and_rebolt();
> +	get_paca()->slb_cache_ptr = 0;
> +}


I think this should do something more like flush_and_reload_slb from
powernv machine check code. We are real mode so should invalidate all
SLBs.

It happens I also need very similar code (without the initial
invalidate) for implementing idle wakeup code in C, so we should move
that function and variants into mm/slb.c IMO.

Thanks,
Nick