[PATCH 04/10] powerpc/64s: disallow system reset vs system reset reentrancy
Nicholas Piggin
npiggin at gmail.com
Tue Dec 20 05:30:05 AEDT 2016
In preparation for using a dedicated stack for system reset interrupts,
prevent a nested system reset from recovering, in order to simplify
code that is called in crash/debug path. This allows a system reset
interrupt to just use the base stack pointer.
Keep an in_nmi nesting counter similarly to the in_mce counter. Consider
the interrrupt non-recoverable if it is taken inside another system
reset.
Interrupt nesting could be allowed similarly to MCE, but system reset
is a special case that's not for normal operation, so simplicity wins
until there is requirement for nested system reset interrupts.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/include/asm/exception-64s.h | 11 ++++++++++
arch/powerpc/include/asm/paca.h | 5 ++++-
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kernel/exceptions-64s.S | 37 +++++++++++++++++++++++++++-----
arch/powerpc/kernel/traps.c | 8 ++++++-
arch/powerpc/xmon/xmon.c | 1 +
6 files changed, 56 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 18eceba135cb..7e47fb67c696 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -214,12 +214,23 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
EXCEPTION_PROLOG_1(area, extra, vec); \
EXCEPTION_PROLOG_PSERIES_1(label, h);
+/* Do not enable RI */
+#define EXCEPTION_PROLOG_PSERIES_NORI(area, label, h, extra, vec) \
+ EXCEPTION_PROLOG_0(area); \
+ EXCEPTION_PROLOG_1(area, extra, vec); \
+ EXCEPTION_PROLOG_PSERIES_1_NORI(label, h);
+
/* Have the PACA in r13 already */
#define EXCEPTION_PROLOG_PSERIES_PACA(area, label, h, extra, vec) \
EXCEPTION_PROLOG_0_PACA(area); \
EXCEPTION_PROLOG_1(area, extra, vec); \
EXCEPTION_PROLOG_PSERIES_1(label, h);
+#define EXCEPTION_PROLOG_PSERIES_PACA_NORI(area, label, h, extra, vec) \
+ EXCEPTION_PROLOG_0_PACA(area); \
+ EXCEPTION_PROLOG_1(area, extra, vec); \
+ EXCEPTION_PROLOG_PSERIES_1_NORI(label, h);
+
#define __KVMTEST(h, n) \
lbz r10,HSTATE_IN_GUEST(r13); \
cmpwi r10,0; \
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 06e96648c1cb..98da152b257b 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -181,12 +181,15 @@ struct paca_struct {
#ifdef CONFIG_PPC_BOOK3S_64
/* Exclusive emergency stack pointer for machine check exception. */
void *mc_emergency_sp;
+
+ u16 in_nmi; /* In nmi handler */
+
/*
* Flag to check whether we are in machine check early handler
* and already using emergency stack.
*/
u16 in_mce;
- u8 hmi_event_available; /* HMI event is available */
+ u8 hmi_event_available; /* HMI event is available */
#endif
/* Stuff for accurate time accounting */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index fa7087a2d825..893da286ecc3 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -244,6 +244,7 @@ int main(void)
#ifdef CONFIG_PPC_BOOK3S_64
DEFINE(PACAMCEMERGSP, offsetof(struct paca_struct, mc_emergency_sp));
DEFINE(PACA_IN_MCE, offsetof(struct paca_struct, in_mce));
+ DEFINE(PACA_IN_NMI, offsetof(struct paca_struct, in_nmi));
#endif
DEFINE(PACAHWCPUID, offsetof(struct paca_struct, hw_cpu_id));
DEFINE(PACAKEXECSTATE, offsetof(struct paca_struct, kexec_state));
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index dd2bb0d785c6..4034f7db73b7 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -118,7 +118,11 @@ EXC_REAL_BEGIN(system_reset, 0x100, 0x200)
SET_SCRATCH0(r13)
GET_PACA(r13)
clrrdi r13,r13,1 /* Last bit of HSPRG0 is set if waking from winkle */
- EXCEPTION_PROLOG_PSERIES_PACA(PACA_EXNMI, system_reset_common,
+ /*
+ * MSR_RI is not enabled, because PACA_EXNMI and nmi stack is
+ * being used, so a nested NMI exception would corrupt it.
+ */
+ EXCEPTION_PROLOG_PSERIES_PACA_NORI(PACA_EXNMI, system_reset_common,
EXC_STD, IDLETEST, 0x100)
EXC_REAL_END(system_reset, 0x100, 0x200)
@@ -154,9 +158,31 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
#endif
EXC_COMMON_BEGIN(system_reset_common)
+ /*
+ * Increment paca->in_nmi then enable MSR_RI. SLB or MCE will be able
+ * to recover, but nested NMI will notice in_nmi and not recover
+ * because of the use of the NMI stack. in_nmi reentrancy is tested in
+ * system_reset_exception.
+ */
+ lhz r10,PACA_IN_NMI(r13)
+ addi r10,r10,1
+ sth r10,PACA_IN_NMI(r13)
+ li r10,MSR_RI
+ mtmsrd r10,1
+
EXCEPTION_COMMON(PACA_EXNMI, 0x100,
- system_reset, system_reset_exception,
- ret_from_except, ADD_NVGPRS;ADD_RECONCILE)
+ system_reset, system_reset_exception, 1f,
+ ADD_NVGPRS;ADD_RECONCILE)
+1: /* EXCEPTION_COMMON continues here */
+
+ /*
+ * The stack is no longer in use, decrement in_nmi.
+ */
+ lhz r10,PACA_IN_NMI(r13)
+ subi r10,r10,1
+ sth r10,PACA_IN_NMI(r13)
+
+ b ret_from_except
#ifdef CONFIG_PPC_PSERIES
/*
@@ -164,8 +190,9 @@ EXC_COMMON_BEGIN(system_reset_common)
*/
TRAMP_REAL_BEGIN(system_reset_fwnmi)
SET_SCRATCH0(r13) /* save r13 */
- EXCEPTION_PROLOG_PSERIES(PACA_EXNMI, system_reset_common, EXC_STD,
- NOTEST, 0x100)
+ /* See comment at system_reset exception */
+ EXCEPTION_PROLOG_PSERIES_NORI(PACA_EXNMI, system_reset_common,
+ EXC_STD, NOTEST, 0x100)
#endif /* CONFIG_PPC_PSERIES */
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 4239aaf74886..802aa6bbe97b 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -281,11 +281,17 @@ void system_reset_exception(struct pt_regs *regs)
/* See if any machine dependent calls */
if (ppc_md.system_reset_exception) {
if (ppc_md.system_reset_exception(regs))
- return;
+ goto out;
}
die("System Reset", regs, SIGABRT);
+out:
+#ifdef CONFIG_PPC_BOOK3S_64
+ BUG_ON(get_paca()->in_nmi == 0);
+ if (get_paca()->in_nmi > 1)
+ panic("Unrecoverable nested System Reset");
+#endif
/* Must die if the interrupt is not recoverable */
if (!(regs->msr & MSR_RI))
panic("Unrecoverable System Reset");
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 9c0e17cf6886..832cbc097416 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -2228,6 +2228,7 @@ static void dump_one_paca(int cpu)
DUMP(p, emergency_sp, "p");
#ifdef CONFIG_PPC_BOOK3S_64
DUMP(p, mc_emergency_sp, "p");
+ DUMP(p, in_nmi, "x");
DUMP(p, in_mce, "x");
DUMP(p, hmi_event_available, "x");
#endif
--
2.11.0
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