[PATCH 3.13.y-ckt 127/139] powerpc/powernv: Switch off MMU before entering nap/sleep/rvwinkle mode

Kamal Mostafa kamal at canonical.com
Thu Jan 29 09:21:10 AEDT 2015

3.13.11-ckt15 -stable review patch.  If anyone has any objections, please let me know.


From: Paul Mackerras <paulus at samba.org>

commit 8117ac6a6c2fa0f847ff6a21a1f32c8d2c8501d0 upstream.

Currently, when going idle, we set the flag indicating that we are in
nap mode (paca->kvm_hstate.hwthread_state) and then execute the nap
(or sleep or rvwinkle) instruction, all with the MMU on.  This is bad
for two reasons: (a) the architecture specifies that those instructions
must be executed with the MMU off, and in fact with only the SF, HV, ME
and possibly RI bits set, and (b) this introduces a race, because as
soon as we set the flag, another thread can switch the MMU to a guest
context.  If the race is lost, this thread will typically start looping
on relocation-on ISIs at 0xc...4400.

This fixes it by setting the MSR as required by the architecture before
setting the flag or executing the nap/sleep/rvwinkle instruction.

[ shreyas at linux.vnet.ibm.com: Edited to handle LE ]
Signed-off-by: Paul Mackerras <paulus at samba.org>
Signed-off-by: Shreyas B. Prabhu <shreyas at linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: linuxppc-dev at lists.ozlabs.org
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 arch/powerpc/include/asm/reg.h    |  2 ++
 arch/powerpc/kernel/idle_power7.S | 17 +++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 637f513..663e5c2 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -118,8 +118,10 @@
 #define __MSR		(MSR_ME | MSR_RI | MSR_IR | MSR_DR | MSR_ISF |MSR_HV)
 #ifdef __BIG_ENDIAN__
 #define MSR_		__MSR
+#define MSR_IDLE	(MSR_ME | MSR_SF | MSR_HV)
 #define MSR_		(__MSR | MSR_LE)
 #define MSR_KERNEL	(MSR_ | MSR_64BIT)
 #define MSR_USER32	(MSR_ | MSR_PR | MSR_EE)
diff --git a/arch/powerpc/kernel/idle_power7.S b/arch/powerpc/kernel/idle_power7.S
index 847e40e..1fb7fee 100644
--- a/arch/powerpc/kernel/idle_power7.S
+++ b/arch/powerpc/kernel/idle_power7.S
@@ -84,6 +84,23 @@ _GLOBAL(power7_nap)
 	std	r9,_MSR(r1)
 	std	r1,PACAR1(r13)
+	/*
+	 * Go to real mode to do the nap, as required by the architecture.
+	 * Also, we need to be in real mode before setting hwthread_state,
+	 * because as soon as we do that, another thread can switch
+	 * the MMU context to the guest.
+	 */
+	li	r6, MSR_RI
+	andc	r6, r9, r6
+	LOAD_REG_ADDR(r7, power7_enter_nap_mode)
+	mtmsrd	r6, 1		/* clear RI before setting SRR0/1 */
+	mtspr	SPRN_SRR0, r7
+	mtspr	SPRN_SRR1, r5
+	rfid
+	.globl	power7_enter_nap_mode
 	/* Tell KVM we're napping */

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