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

[Nicholas Piggin <npiggin@gmail.com>]

On Thu, 12 Jul 2018 15:41:13 +0200
Michal Such=C3=A1nek <msuchanek@suse.de> wrote:

> On Tue, 3 Jul 2018 08:08:14 +1000
> "Nicholas Piggin" <npiggin@gmail.com> wrote:
>=20
> > On Mon, 02 Jul 2018 11:17:06 +0530
> > Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:
> >  =20
> > > From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> > >=20
> > > 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.
> > >=20
> > > Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> > > ---
> > >  arch/powerpc/include/asm/book3s/64/mmu-hash.h |    1=20
> > >  arch/powerpc/include/asm/machdep.h            |    1=20
> > >  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=20
> > >  arch/powerpc/platforms/pseries/pseries.h      |    1=20
> > >  arch/powerpc/platforms/pseries/ras.c          |   51
> > > +++++++++++++++++++++++++
> > > arch/powerpc/platforms/pseries/setup.c        |    1 9 files
> > > changed, 116 insertions(+), 4 deletions(-)  =20
> >=20
> >  =20
> > > +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 */   =20
> >=20
> > Is there any reason you can't use the existing
> > machine_check_powernv_early code to do all this?
> >  =20
> > > 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 =3D 0;
> > > =20
> > > -	__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);
> > > =20
> > > -	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 =3D ppc_md.machine_check_early(regs);
> > > +	else if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
> > >  		handled =3D
> > > cur_cpu_spec->machine_check_early(regs);   =20
> >=20
> > Would be good to add a powernv ppc_md handler which does the
> > cur_cpu_spec->machine_check_early() call now that other platforms are
> > calling this code. Because those aren't valid as a fallback call, but
> > specific to powernv.
> >  =20
>=20
> Something like this (untested)?

Sorry, some emails fell through the cracks. Yes exactly like this would
be good. If you can add a quick changelog and SOB, and
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks,
Nick

>=20
> Subject: [PATCH] powerpc/powernv: define platform MCE handler.
>=20
> ---
>  arch/powerpc/kernel/mce.c              |  3 ---
>  arch/powerpc/platforms/powernv/setup.c | 11 +++++++++++
>  2 files changed, 11 insertions(+), 3 deletions(-)
>=20
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index 221271c96a57..ae17d8aa60c4 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -498,12 +498,9 @@ long machine_check_early(struct pt_regs *regs)
> =20
>  	/*
>  	 * 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 =3D ppc_md.machine_check_early(regs);
> -	else if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
> -		handled =3D cur_cpu_spec->machine_check_early(regs);
>  	return handled;
>  }
> =20
> diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platfo=
rms/powernv/setup.c
> index f96df0a25d05..b74c93bc2e55 100644
> --- a/arch/powerpc/platforms/powernv/setup.c
> +++ b/arch/powerpc/platforms/powernv/setup.c
> @@ -431,6 +431,16 @@ static unsigned long pnv_get_proc_freq(unsigned int =
cpu)
>  	return ret_freq;
>  }
> =20
> +static long pnv_machine_check_early(struct pt_regs *regs)
> +{
> +	long handled =3D 0;
> +
> +	if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
> +		handled =3D cur_cpu_spec->machine_check_early(regs);
> +
> +	return handled;
> +}
> +
>  define_machine(powernv) {
>  	.name			=3D "PowerNV",
>  	.probe			=3D pnv_probe,
> @@ -442,6 +452,7 @@ define_machine(powernv) {
>  	.machine_shutdown	=3D pnv_shutdown,
>  	.power_save             =3D NULL,
>  	.calibrate_decr		=3D generic_calibrate_decr,
> +	.machine_check_early	=3D pnv_machine_check_early,
>  #ifdef CONFIG_KEXEC_CORE
>  	.kexec_cpu_down		=3D pnv_kexec_cpu_down,
>  #endif