Subject: Re: [PATCH 4/8] powerpc/64s: fix POWER9 machine check handler from stop state

From: Gautham R Shenoy <[email-masked]>
Date: Thu, 16 Mar 2017 18:49:07 +0530

Hi,

On Thu, Mar 16, 2017 at 11:05:20PM +1000, Nicholas Piggin wrote:
> On Thu, 16 Mar 2017 18:10:48 +0530
> Mahesh Jagannath Salgaonkar <[email-masked]> wrote:
> 
> > On 03/14/2017 02:53 PM, Nicholas Piggin wrote:
> > > The ISA specifies power save wakeup can cause a machine check interrupt.
> > > The machine check handler currently has code to handle that for POWER8,
> > > but POWER9 crashes when trying to execute the P8 style sleep
> > > instructions.
> > > 
> > > So queue up the machine check, then call into the idle code to wake up
> > > as the system reset interrupt does, rather than attempting to sleep
> > > again without going through the main idle path.
> > > 
> > > Reviewed-by: Gautham R. Shenoy <[email-masked]>
> > > Signed-off-by: Nicholas Piggin <[email-masked]>
> > > ---
> > >  arch/powerpc/include/asm/reg.h       |  1 +
> > >  arch/powerpc/kernel/exceptions-64s.S | 69 ++++++++++++++++++------------------
> > >  2 files changed, 35 insertions(+), 35 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> > > index fc879fd6bdae..8bbdfacce970 100644
> > > --- a/arch/powerpc/include/asm/reg.h
> > > +++ b/arch/powerpc/include/asm/reg.h
> > > @@ -656,6 +656,7 @@
> > >  #define   SRR1_ISI_PROT		0x08000000 /* ISI: Other protection fault */
> > >  #define   SRR1_WAKEMASK		0x00380000 /* reason for wakeup */
> > >  #define   SRR1_WAKEMASK_P8	0x003c0000 /* reason for wakeup on POWER8 and 9 */
> > > +#define   SRR1_WAKEMCE_RESVD	0x003c0000 /* Unused/reserved value used by MCE wakeup to indicate cause to idle wakeup handler */
> > >  #define   SRR1_WAKESYSERR	0x00300000 /* System error */
> > >  #define   SRR1_WAKEEE		0x00200000 /* External interrupt */
> > >  #define   SRR1_WAKEHVI		0x00240000 /* Hypervisor Virtualization Interrupt (P9) */
> > > diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> > > index e390fcd04bcb..5779d2d6a192 100644
> > > --- a/arch/powerpc/kernel/exceptions-64s.S
> > > +++ b/arch/powerpc/kernel/exceptions-64s.S
> > > @@ -306,6 +306,33 @@ EXC_COMMON_BEGIN(machine_check_common)
> > >  	/* restore original r1. */			\
> > >  	ld	r1,GPR1(r1)
> > > 
> > > +#ifdef CONFIG_PPC_P7_NAP
> > > +EXC_COMMON_BEGIN(machine_check_idle_common)
> > > +	bl	machine_check_queue_event
> > > +	/*
> > > +	 * Queue the machine check, then reload SRR1 and use it to set
> > > +	 * CR3 according to pnv_powersave_wakeup convention.
> > > +	 */
> > > +	ld	r12,_MSR(r1)
> > > +	rlwinm	r11,r12,47-31,30,31
> > > +	cmpwi	cr3,r11,2
> > > +
> > > +	/*
> > > +	 * Now put SRR1_WAKEMCE_RESVD into SRR1, allows it to follow the
> > > +	 * system reset wakeup code.
> > > +	 */
> > > +	oris	r12,r12,SRR1_WAKEMCE_RESVD@h
> > > +	mtspr	SPRN_SRR1,r12
> > > +	std	r12,_MSR(r1)
> > > +
> > > +	/*
> > > +	 * Decrement MCE nesting after finishing with the stack.
> > > +	 */
> > > +	lhz	r11,PACA_IN_MCE(r13)
> > > +	subi	r11,r11,1
> > > +	sth	r11,PACA_IN_MCE(r13)  
> > 
> > Looks like we are not winding up.. Shouldn't we ? What if we may end up
> > in pnv_wakeup_noloss() which assumes that no GPRs are lost. Am I missing
> > anything ?

Nice catch! This can occur if SRR1[46:47] == 0b01.

>
> Hmm, no I think you're right. Thanks, good catch. But can we do it with
> just setting PACA_NAPSTATELOST?

Unconditionally setting PACA_NAPSTATELOST should be sufficient.

> 
> > 
> > > +	b	pnv_powersave_wakeup
> > > +#endif
> > >  	/*  
> > 
> > [...]
> > 
> > Rest looks good to me.
> > 
> > Reviewed-by: Mahesh J Salgaonkar <[email-masked]>
> 
> Thanks,
> Nick
>