[PATCH 3.16 332/366] powerpc/64s: Clear PCR on boot

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Neuling <mikey@xxxxxxxxxxx>

commit faf37c44a105f3608115785f17cbbf3500f8bc71 upstream.

Clear the PCR (Processor Compatibility Register) on boot to ensure we
are not running in a compatibility mode.

We've seen this cause problems when a crash (and kdump) occurs while
running compat mode guests. The kdump kernel then runs with the PCR
set and causes problems. The symptom in the kdump kernel (also seen in
petitboot after fast-reboot) is early userspace programs taking
sigills on newer instructions (seen in libc).

Signed-off-by: Michael Neuling <mikey@xxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
[bwh: Backported to 3.16: Drop changes in __{setup,restore}_cpu_power9
 and __restore_cpu_cpufeatures()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/powerpc/kernel/cpu_setup_power.S
+++ b/arch/powerpc/kernel/cpu_setup_power.S
@@ -27,6 +27,7 @@ _GLOBAL(__setup_cpu_power7)
 	beqlr
 	li	r0,0
 	mtspr	SPRN_LPID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr	r3,SPRN_LPCR
 	bl	__init_LPCR
 	bl	__init_tlb_power7
@@ -40,6 +41,7 @@ _GLOBAL(__restore_cpu_power7)
 	beqlr
 	li	r0,0
 	mtspr	SPRN_LPID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr	r3,SPRN_LPCR
 	bl	__init_LPCR
 	bl	__init_tlb_power7
@@ -55,6 +57,7 @@ _GLOBAL(__setup_cpu_power8)
 	beqlr
 	li	r0,0
 	mtspr	SPRN_LPID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr	r3,SPRN_LPCR
 	ori	r3, r3, LPCR_PECEDH
 	bl	__init_LPCR
@@ -74,6 +77,7 @@ _GLOBAL(__restore_cpu_power8)
 	beqlr
 	li	r0,0
 	mtspr	SPRN_LPID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr   r3,SPRN_LPCR
 	ori	r3, r3, LPCR_PECEDH
 	bl	__init_LPCR