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powerpc/64s: Fix stack setup in watchdog soft_nmi_common()

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The watchdog soft-NMI exception stack setup loads a stack pointer
twice, which is an obvious error. It ends up using the system reset
interrupt (true-NMI) stack, which is also a bug because the watchdog
could be preempted by a system reset interrupt that overwrites the
NMI stack.

Change the soft-NMI to use the "emergency stack". The current kernel
stack is not used, because of the longer-term goal to prevent
asynchronous stack access using soft-disable.

Fixes: 2104180a53 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2017-07-29 22:50:27 +10:00 committed by Michael Ellerman
parent bb272221e9
commit cc491f1d35
1 changed files with 9 additions and 1 deletions
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10
arch/powerpc/kernel/exceptions-64s.S
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@ -1325,10 +1325,18 @@ EXC_VIRT_NONE(0x5800, 0x100)
std r10,PACA_EXGEN+EX_R13(r13); \
EXCEPTION_PROLOG_PSERIES_1(soft_nmi_common, _H)
/*
* Branch to soft_nmi_interrupt using the emergency stack. The emergency
* stack is one that is usable by maskable interrupts so long as MSR_EE
* remains off. It is used for recovery when something has corrupted the
* normal kernel stack, for example. The "soft NMI" must not use the process
* stack because we want irq disabled sections to avoid touching the stack
* at all (other than PMU interrupts), so use the emergency stack for this,
* and run it entirely with interrupts hard disabled.
*/
EXC_COMMON_BEGIN(soft_nmi_common)
mr r10,r1
ld r1,PACAEMERGSP(r13)
ld r1,PACA_NMI_EMERG_SP(r13)
subi r1,r1,INT_FRAME_SIZE
EXCEPTION_COMMON_NORET_STACK(PACA_EXGEN, 0x900,
system_reset, soft_nmi_interrupt,