Re: [v3 PATCH 4/5] powerpc/pseries: Dump and flush SLB contents on SLB MCE errors.

[Nicholas Piggin <npiggin@gmail.com>]

On Thu, 07 Jun 2018 22:58:55 +0530
Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:

> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> 
> If we get a machine check exceptions due to SLB errors then dump the
> current SLB contents which will be very much helpful in debugging the
> root cause of SLB errors. On pseries, as of today system crashes on 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. This patch
> fixes that also.

So pseries never flushed SLB and reloaded in response to multi hit
errors? This seems like quite a good improvement then. I like
dumping SLB too.

It's a bit annoying we can't share the same code with xmon really,
that's okay but I just suggest commenting them both if you take a
copy like this with a note to keep them in synch if you re-post
the series.

> 
> With this patch the console will log SLB contents like below on SLB MCE
> errors:
> 
> [  822.711728] slb contents:

Suggest keeping the same format as the xmon dump (in particular
CPU number, even though it's probably printed elsewhere in the MCE
message it doesn't hurt.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks,
Nick

> [  822.711730] 00 c000000008000000 400ea1b217000500
> [  822.711731]   1T  ESID=   c00000  VSID=      ea1b217 LLP:100
> [  822.711732] 01 d000000008000000 400d43642f000510
> [  822.711733]   1T  ESID=   d00000  VSID=      d43642f LLP:110
> [  822.711734] 09 f000000008000000 400a86c85f000500
> [  822.711736]   1T  ESID=   f00000  VSID=      a86c85f LLP:100
> [  822.711737] 10 00007f0008000000 400d1f26e3000d90
> [  822.711738]   1T  ESID=       7f  VSID=      d1f26e3 LLP:110
> [  822.711739] 11 0000000018000000 000e3615f520fd90
> [  822.711740]  256M ESID=        1  VSID=   e3615f520f LLP:110
> [  822.711740] 12 d000000008000000 400d43642f000510
> [  822.711741]   1T  ESID=   d00000  VSID=      d43642f LLP:110
> [  822.711742] 13 d000000008000000 400d43642f000510
> [  822.711743]   1T  ESID=   d00000  VSID=      d43642f LLP:110
> 
> 
> Suggested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/mmu-hash.h |    1 +
>  arch/powerpc/mm/slb.c                         |   35 +++++++++++++++++++++++++
>  arch/powerpc/platforms/pseries/ras.c          |   29 ++++++++++++++++++++-
>  3 files changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu-hash.h b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
> index 50ed64fba4ae..c0da68927235 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_dump_contents(void);
>  
>  extern void slb_vmalloc_update(void);
>  extern void slb_set_size(u16 size);
> diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
> index 66577cc66dc9..799aa117cec3 100644
> --- a/arch/powerpc/mm/slb.c
> +++ b/arch/powerpc/mm/slb.c
> @@ -145,6 +145,41 @@ void slb_flush_and_rebolt(void)
>  	get_paca()->slb_cache_ptr = 0;
>  }
>  
> +void slb_dump_contents(void)
> +{
> +	int i;
> +	unsigned long e, v;
> +	unsigned long llp;
> +
> +	pr_err("slb contents:\n");
> +	for (i = 0; i < mmu_slb_size; i++) {
> +		asm volatile("slbmfee  %0,%1" : "=r" (e) : "r" (i));
> +		asm volatile("slbmfev  %0,%1" : "=r" (v) : "r" (i));
> +
> +		if (!e && !v)
> +			continue;
> +
> +		pr_err("%02d %016lx %016lx", i, e, v);
> +
> +		if (!(e & SLB_ESID_V)) {
> +			pr_err("\n");
> +			continue;
> +		}
> +		llp = v & SLB_VSID_LLP;
> +		if (v & SLB_VSID_B_1T) {
> +			pr_err("  1T  ESID=%9lx  VSID=%13lx LLP:%3lx\n",
> +				GET_ESID_1T(e),
> +				(v & ~SLB_VSID_B) >> SLB_VSID_SHIFT_1T,
> +				llp);
> +		} else {
> +			pr_err(" 256M ESID=%9lx  VSID=%13lx LLP:%3lx\n",
> +				GET_ESID(e),
> +				(v & ~SLB_VSID_B) >> SLB_VSID_SHIFT,
> +				llp);
> +		}
> +	}
> +}
> +
>  void slb_vmalloc_update(void)
>  {
>  	unsigned long vflags;
> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 2edc673be137..e56759d92356 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -422,6 +422,31 @@ int pSeries_system_reset_exception(struct pt_regs *regs)
>  	return 0; /* need to perform reset */
>  }
>  
> +static int mce_handle_error(struct rtas_error_log *errp)
> +{
> +	struct pseries_errorlog *pseries_log;
> +	struct pseries_mc_errorlog *mce_log;
> +	int disposition = rtas_error_disposition(errp);
> +	uint8_t error_type;
> +
> +	pseries_log = get_pseries_errorlog(errp, PSERIES_ELOG_SECT_ID_MCE);
> +	if (pseries_log == NULL)
> +		goto out;
> +
> +	mce_log = (struct pseries_mc_errorlog *)pseries_log->data;
> +	error_type = rtas_mc_error_type(mce_log);
> +
> +	if ((disposition == RTAS_DISP_NOT_RECOVERED) &&
> +			(error_type == PSERIES_MC_ERROR_TYPE_SLB)) {
> +		slb_dump_contents();
> +		slb_flush_and_rebolt();
> +		disposition = RTAS_DISP_FULLY_RECOVERED;
> +	}
> +
> +out:
> +	return disposition;
> +}
> +
>  /*
>   * See if we can recover from a machine check exception.
>   * This is only called on power4 (or above) and only via
> @@ -434,7 +459,9 @@ int pSeries_system_reset_exception(struct pt_regs *regs)
>  static int recover_mce(struct pt_regs *regs, struct rtas_error_log *err)
>  {
>  	int recovered = 0;
> -	int disposition = rtas_error_disposition(err);
> +	int disposition;
> +
> +	disposition = mce_handle_error(err);
>  
>  	if (!(regs->msr & MSR_RI)) {
>  		/* If MSR_RI isn't set, we cannot recover */
>