Re: [PATCH v6 8/8] powernv/pseries: consolidate code for mce early handling.

[Nicholas Piggin <npiggin@gmail.com>]

On Mon, 9 Jul 2018 18:02:39 +0200
Michal Such=C3=A1nek <msuchanek@suse.de> wrote:

> On Fri, 6 Jul 2018 19:40:24 +1000
> Nicholas Piggin <npiggin@gmail.com> wrote:
>=20
> > On Wed, 04 Jul 2018 23:30:12 +0530
> > Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:
> >  =20
> > > From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> > >=20
> > > Now that other platforms also implements real mode mce handler,
> > > lets consolidate the code by sharing existing powernv machine check
> > > early code. Rename machine_check_powernv_early to
> > > machine_check_common_early and reuse the code.
> > >=20
> > > Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> > > ---
> > >  arch/powerpc/kernel/exceptions-64s.S |   56
> > > +++++++--------------------------- 1 file changed, 11
> > > insertions(+), 45 deletions(-)
> > >=20
> > > diff --git a/arch/powerpc/kernel/exceptions-64s.S
> > > b/arch/powerpc/kernel/exceptions-64s.S index
> > > 0038596b7906..3e877ec55d50 100644 ---
> > > a/arch/powerpc/kernel/exceptions-64s.S +++
> > > b/arch/powerpc/kernel/exceptions-64s.S @@ -243,14 +243,13 @@
> > > EXC_REAL_BEGIN(machine_check, 0x200, 0x100)
> > > SET_SCRATCH0(r13)		/* save r13 */
> > > EXCEPTION_PROLOG_0(PACA_EXMC) BEGIN_FTR_SECTION
> > > -	b	machine_check_powernv_early
> > > +	b	machine_check_common_early
> > >  FTR_SECTION_ELSE
> > >  	b	machine_check_pSeries_0
> > >  ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
> > >  EXC_REAL_END(machine_check, 0x200, 0x100)
> > >  EXC_VIRT_NONE(0x4200, 0x100)
> > > -TRAMP_REAL_BEGIN(machine_check_powernv_early)
> > > -BEGIN_FTR_SECTION
> > > +TRAMP_REAL_BEGIN(machine_check_common_early)
> > >  	EXCEPTION_PROLOG_1(PACA_EXMC, NOTEST, 0x200)
> > >  	/*
> > >  	 * Register contents:
> > > @@ -306,7 +305,9 @@ BEGIN_FTR_SECTION
> > >  	/* Save r9 through r13 from EXMC save area to stack frame.
> > > */ EXCEPTION_PROLOG_COMMON_2(PACA_EXMC)
> > >  	mfmsr	r11			/* get MSR value */
> > > +BEGIN_FTR_SECTION
> > >  	ori	r11,r11,MSR_ME		/* turn on ME bit
> > > */ +END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
> > >  	ori	r11,r11,MSR_RI		/* turn on RI bit
> > > */ LOAD_HANDLER(r12, machine_check_handle_early)
> > >  1:	mtspr	SPRN_SRR0,r12
> > > @@ -325,7 +326,6 @@ BEGIN_FTR_SECTION
> > >  	andc	r11,r11,r10		/* Turn off MSR_ME
> > > */ b	1b
> > >  	b	.	/* prevent speculative execution */
> > > -END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
> > > =20
> > >  TRAMP_REAL_BEGIN(machine_check_pSeries)
> > >  	.globl machine_check_fwnmi
> > > @@ -333,7 +333,7 @@ machine_check_fwnmi:
> > >  	SET_SCRATCH0(r13)		/* save r13 */
> > >  	EXCEPTION_PROLOG_0(PACA_EXMC)
> > >  BEGIN_FTR_SECTION
> > > -	b	machine_check_pSeries_early
> > > +	b	machine_check_common_early
> > >  END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
> > >  machine_check_pSeries_0:
> > >  	EXCEPTION_PROLOG_1(PACA_EXMC, KVMTEST_PR, 0x200)
> > > @@ -346,45 +346,6 @@ machine_check_pSeries_0:
> > > =20
> > >  TRAMP_KVM_SKIP(PACA_EXMC, 0x200)
> > > =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 */ -
> > > -	/* 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
> > > @@ -483,6 +444,9 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
> > >  	bl	machine_check_early
> > >  	std	r3,RESULT(r1)	/* Save result */
> > >  	ld	r12,_MSR(r1)
> > > +BEGIN_FTR_SECTION
> > > +	bne	9f			/* pSeries: continue
> > > to V mode. */ +END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)   =20
> >=20
> > Should this be "b 9f" ? Although...
> >  =20
> > > =20
> > >  #ifdef	CONFIG_PPC_P7_NAP
> > >  	/*
> > > @@ -564,7 +528,9 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
> > >  9:
> > >  	/* Deliver the machine check to host kernel in V mode. */
> > >  	MACHINE_CHECK_HANDLER_WINDUP
> > > -	b	machine_check_pSeries
> > > +	SET_SCRATCH0(r13)		/* save r13 */
> > > +	EXCEPTION_PROLOG_0(PACA_EXMC)
> > > +	b	machine_check_pSeries_0   =20
> >=20
> > I'm not sure that's quite right. You're missing out testing the result
> > of the early handler call? Is this buggy in existing code too? We
> > should be testing that result in all cases, shouldn't we? But it
> > doesn't seem like we are. =20
>=20
> At least for the pSeries case the result of realmode handler is stored
> in the MCE log data. Both the real and virtual part of the handler
> should be called in any case. They do different and independent things.

Hmm, well the return code of the function in the powernv case is put
into regs->result which is missing here, but I guess it gets picked
up again when the pseries code is consolidated back with powernv.

But... maybe that result is not actually used anywhere though. I
guess that's okay, maybe we should just make it return void though.

We want to avoid the case of going to virtual mode if we have errors
in the SLB or TLB that causes a recursive MCE, but the recursion
limit will eventually catch that and checkstop us which might be
the sanest option.

Thanks,
Nick