powerpc/64s: Disallow system reset vs system reset reentrancy

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@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 63a309a432ad562f7c3cf0bc64a782a0e853fe41..59134ebd7d495c17237e91e154a306e8fb5efc1e 100644 (file)
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -275,6 +275,12 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 
 #endif
 
+/* 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);
+
 
 #define __KVM_HANDLER(area, h, n)                                      \
        BEGIN_FTR_SECTION_NESTED(947)                                   \

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 601e2327dd8c98bc5bbcd921bd3c565b78a62302..b1197c1affacd153d7c99a0286e498fb31fae229 100644 (file)
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -187,12 +187,15 @@ 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 46732ee70b43069e28bc178c17c9e97faa80ae3a..1466e96d36cff6fdf3c1ea38bc6d5e83c190e181 100644 (file)
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -235,6 +235,7 @@ int main(void)
 #ifdef CONFIG_PPC_BOOK3S_64
        OFFSET(PACAMCEMERGSP, paca_struct, mc_emergency_sp);
        OFFSET(PACA_IN_MCE, paca_struct, in_mce);
+       OFFSET(PACA_IN_NMI, paca_struct, in_nmi);
 #endif
        OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id);
        OFFSET(PACAKEXECSTATE, paca_struct, kexec_state);

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3a654b1f24e9b00256c71d0f3ad9257cbe6979ae..4be62568fbc27b5700bc694679ab22fa1a2f5f11 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -116,7 +116,11 @@ EXC_VIRT_NONE(0x4000, 0x100)
 
 EXC_REAL_BEGIN(system_reset, 0x100, 0x100)
        SET_SCRATCH0(r13)
-       EXCEPTION_PROLOG_PSERIES(PACA_EXNMI, system_reset_common, EXC_STD,
+       /*
+        * 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_NORI(PACA_EXNMI, system_reset_common, EXC_STD,
                                 IDLETEST, 0x100)
 
 EXC_REAL_END(system_reset, 0x100, 0x100)
@@ -128,9 +132,31 @@ EXC_COMMON_BEGIN(system_reset_idle_common)
 #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
 /*
@@ -138,8 +164,9 @@ 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 76f6045b021bc3e01ca32dc3cecc20c4ec129a15..2393d3c462360e0e95713eba195427e373b4f566 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -282,11 +282,17 @@ 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 2b21e90fff8dcabfa32246622f154d997f5549ad..99348a2961b83a4d22c89074142f18ecf4ed6ac5 100644 (file)
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -2236,6 +2236,7 @@ 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