Commit 1945bc45 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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powerpc/64s: Fix POWER9 machine check handler from stop state

The ISA specifies power save wakeup due to a machine check exception can
cause a machine check interrupt (rather than the usual system reset

The machine check handler copes with this by doing low level machine
check recovery without restoring full state from idle, then queues up a
machine check event for logging, then directly executes the same idle
instruction it woke from. This minimises the work done before recovery
is performed.

The problem is that it requires machine specific instructions and
knowledge of the book3s idle code. Currently it only has code to handle
POWER8 idle, so POWER9 crashes when trying to execute the P8 idle
instructions which don't exist in ISAv3.0B.

cpu 0x0: Vector: e40 (Emulation Assist) at [c0000000008f3810]
    pc: c000000000008380: machine_check_handle_early+0x130/0x2f0
    lr: c00000000053a098: stop_loop+0x68/0xd0
    sp: c0000000008f3a90
   msr: 9000000000081001
  current = 0xc0000000008a1080
  paca    = 0xc00000000ffd0000   softe: 0        irq_happened: 0x01
    pid   = 0, comm = swapper/0

Instead of going to sleep after recovery, do the usual idle wakeup and
state restoration by calling into the normal idle wakeup path. This
reuses the normal idle wakeup paths.
Reviewed-by: default avatarGautham R. Shenoy <>
Reviewed-by: default avatarMahesh J Salgaonkar <>
Signed-off-by: default avatarNicholas Piggin <>
Signed-off-by: default avatarMichael Ellerman <>
parent 10101aa9
......@@ -659,6 +659,7 @@
#define SRR1_ISI_PROT 0x08000000 /* ISI: Other protection fault */
#define SRR1_WAKEMASK 0x00380000 /* reason for wakeup */
#define SRR1_WAKEMASK_P8 0x003c0000 /* reason for wakeup on POWER8 and 9 */
#define SRR1_WAKEMCE_RESVD 0x003c0000 /* Unused/reserved value used by MCE wakeup to indicate cause to idle wakeup handler */
#define SRR1_WAKESYSERR 0x00300000 /* System error */
#define SRR1_WAKEEE 0x00200000 /* External interrupt */
#define SRR1_WAKEHVI 0x00240000 /* Hypervisor Virtualization Interrupt (P9) */
......@@ -178,6 +178,12 @@ BEGIN_FTR_SECTION
* NOTE: We are here with MSR_ME=0 (off), which means we risk a
* checkstop if we get another machine check exception before we do
* rfid with MSR_ME=1.
* This interrupt can wake directly from idle. If that is the case,
* the machine check is handled then the idle wakeup code is called
* to restore state. In that case, the POWER9 DD1 idle PACA workaround
* is not applied in the early machine check code, which will cause
* bugs.
mr r11,r1 /* Save r1 */
lhz r10,PACA_IN_MCE(r13)
......@@ -306,6 +312,37 @@ EXC_COMMON_BEGIN(machine_check_common)
/* restore original r1. */ \
ld r1,GPR1(r1)
* This is an idle wakeup. Low level machine check has already been
* done. Queue the event then call the idle code to do the wake up.
bl machine_check_queue_event
* We have not used any non-volatile GPRs here, and as a rule
* most exception code including machine check does not.
* Therefore PACA_NAPSTATELOST does not need to be set. Idle
* wakeup will restore volatile registers.
* Load the original SRR1 into r3 for pnv_powersave_wakeup_mce.
* Then decrement MCE nesting after finishing with the stack.
ld r3,_MSR(r1)
lhz r11,PACA_IN_MCE(r13)
subi r11,r11,1
sth r11,PACA_IN_MCE(r13)
/* Turn off the RI bit because SRR1 is used by idle wakeup code. */
/* Recoverability could be improved by reducing the use of SRR1. */
li r11,0
mtmsrd r11,1
b pnv_powersave_wakeup_mce
* Handle machine check early in real mode. We come here with
* ME=1, MMU (IR=0 and DR=0) off and using MC emergency stack.
......@@ -318,6 +355,7 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
bl machine_check_early
std r3,RESULT(r1) /* Save result */
ld r12,_MSR(r1)
* Check if thread was in power saving mode. We come here when any
......@@ -328,43 +366,14 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
* Go back to nap/sleep/winkle mode again if (b) is true.
rlwinm. r11,r12,47-31,30,31 /* Was it in power saving mode? */
beq 4f /* No, it wasn't */
/* Thread was in power saving mode. Go back to nap again. */
cmpwi r11,2
blt 3f
/* Supervisor/Hypervisor state loss */
li r0,1
3: bl machine_check_queue_event
ld r1,PACAR1(r13)
* Check what idle state this CPU was in and go back to same mode
* again.
bgt 10f
/* No return */
bgt 2f
/* No return */
* Go back to winkle. Please note that this thread was woken up in
* machine check from winkle and have not restored the per-subcore
* state.
/* No return */
rlwinm. r11,r12,47-31,30,31
beq- 4f
BRANCH_TO_COMMON(r10, machine_check_idle_common)
* Check if we are coming from hypervisor userspace. If yes then we
* continue in host kernel in V mode to deliver the MC event.
......@@ -415,6 +415,31 @@ power9_dd1_recover_paca:
* Called from machine check handler for powersave wakeups.
* Low level machine check processing has already been done. Now just
* go through the wake up path to get everything in order.
* r3 - The original SRR1 value.
* Original SRR[01] have been clobbered.
* MSR_RI is clear.
.global pnv_powersave_wakeup_mce
/* Set cr3 for pnv_powersave_wakeup */
rlwinm r11,r3,47-31,30,31
cmpwi cr3,r11,2
* Now put the original SRR1 with SRR1_WAKEMCE_RESVD as the wake
* reason into SRR1, which allows reuse of the system reset wakeup
* code without being mistaken for another type of wakeup.
oris r3,r3,SRR1_WAKEMCE_RESVD@h
mtspr SPRN_SRR1,r3
b pnv_powersave_wakeup
* Called from reset vector for powersave wakeups.
* cr3 - set to gt if waking up with partial/complete hypervisor state loss
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