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Commit cc491f1d authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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powerpc/64s: Fix stack setup in watchdog soft_nmi_common() 



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: 2104180a ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent bb272221

arch/powerpc/kernel/exceptions-64s.S

+9 −1
Original line number Diff line number Diff line
@@ -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,