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Revert "powerpc/64s/idle: POWER9 ESL=0 stop avoid save/restore overhead"

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As described in that commit:

  When stop is executed with EC=ESL=0, it appears to execute like a
  normal instruction (resuming from NIP when woken by interrupt). So
  all the save/restore handling can be avoided completely.

This is true, except in the case of an NMI interrupt (sreset or
machine check) interrupting the instruction. In that case, the NMI
gets an "interrupt occurred while the processor was in power-saving
mode" indication. The power-save wakeup code uses that bit to decide
whether to restore some registers (e.g., LR). Because these are no
longer saved, this causes random register corruption.

It may be possible to restore this optimisation by detecting the case
of no register loss on the wakeup side, and avoid restoring in that
case, but that's not a minor fix because the wakeup code itself uses
some registers that would be live (e.g., LR).

Fixes: b9ee31e100 ("powerpc/64s/idle: POWER9 ESL=0 stop avoid save/restore overhead")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Michael Ellerman 2018-04-05 16:03:39 +10:00
parent 07c3d9eaa4
commit a67cc594df
1 changed files with 29 additions and 16 deletions
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45
arch/powerpc/kernel/idle_book3s.S
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@ -324,8 +324,32 @@ enter_winkle:
/*
* r3 - PSSCR value corresponding to the requested stop state.
*/
power_enter_stop_esl:
power_enter_stop:
/*
* Check if we are executing the lite variant with ESL=EC=0
*/
andis. r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
clrldi r3,r3,60 /* r3 = Bits[60:63] = Requested Level (RL) */
bne .Lhandle_esl_ec_set
PPC_STOP
li r3,0 /* Since we didn't lose state, return 0 */
std r3, PACA_REQ_PSSCR(r13)
/*
* pnv_wakeup_noloss() expects r12 to contain the SRR1 value so
* it can determine if the wakeup reason is an HMI in
* CHECK_HMI_INTERRUPT.
*
* However, when we wakeup with ESL=0, SRR1 will not contain the wakeup
* reason, so there is no point setting r12 to SRR1.
*
* Further, we clear r12 here, so that we don't accidentally enter the
* HMI in pnv_wakeup_noloss() if the value of r12[42:45] == WAKE_HMI.
*/
li r12, 0
b pnv_wakeup_noloss
.Lhandle_esl_ec_set:
BEGIN_FTR_SECTION
/*
* POWER9 DD2.0 or earlier can incorrectly set PMAO when waking up after
@ -417,32 +441,21 @@ _GLOBAL(power9_offline_stop)
/* fall through */
_GLOBAL(power9_idle_stop)
mtspr SPRN_PSSCR,r3
/*
* The ESL=EC=0 case does not wake up at 0x100, and it does not
* allow SMT mode switching, so it does not require PSSCR to be
* saved.
*/
andis. r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
bne 1f
PPC_STOP
li r3,0 /* Since we didn't lose state, return 0 */
blr
1:
std r3, PACA_REQ_PSSCR(r13)
#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
BEGIN_FTR_SECTION
sync
lwz r5, PACA_DONT_STOP(r13)
cmpwi r5, 0
bne 2f
bne 1f
END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
#endif
LOAD_REG_ADDR(r4,power_enter_stop_esl)
mtspr SPRN_PSSCR,r3
LOAD_REG_ADDR(r4,power_enter_stop)
b pnv_powersave_common
/* No return */
#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
2:
1:
/*
* We get here when TM / thread reconfiguration bug workaround
* code wants to get the CPU into SMT4 mode, and therefore