[PATCH 4.9] powerpc/64s: Clear PCR on boot

[PATCH 4.9] powerpc/64s: Clear PCR on boot

[Michael Neuling]

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@neuling.org>
Cc: stable@vger.kernel.org # v4.9
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
--

Greg, This is a backport for v4.9 only since the original patch didn't
apply.

Commit faf37c44a105f3608115785f17cbbf3500f8bc71 upstream.
---
 arch/powerpc/kernel/cpu_setup_power.S | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/cpu_setup_power.S b/arch/powerpc/kernel/cpu_setup_power.S
index 9e05c8828e..ff45d007d1 100644
--- a/arch/powerpc/kernel/cpu_setup_power.S
+++ b/arch/powerpc/kernel/cpu_setup_power.S
@@ -28,6 +28,7 @@ _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
@@ -41,6 +42,7 @@ _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
@@ -57,6 +59,7 @@ _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
@@ -78,6 +81,7 @@ _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
@@ -98,6 +102,7 @@ _GLOBAL(__setup_cpu_power9)
 	li	r0,0
 	mtspr	SPRN_LPID,r0
 	mtspr	SPRN_PID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr	r3,SPRN_LPCR
 	LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE)
 	or	r3, r3, r4
@@ -121,6 +126,7 @@ _GLOBAL(__restore_cpu_power9)
 	li	r0,0
 	mtspr	SPRN_LPID,r0
 	mtspr	SPRN_PID,r0
+	mtspr	SPRN_PCR,r0
 	mfspr   r3,SPRN_LPCR
 	LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE)
 	or	r3, r3, r4
-- 
2.17.0

Re: [PATCH 4.9] powerpc/64s: Clear PCR on boot

[Greg KH]

On Tue, May 29, 2018 at 01:56:29PM +1000, Michael Neuling wrote:
> 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@neuling.org>
> Cc: stable@vger.kernel.org # v4.9
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> --
> 
> Greg, This is a backport for v4.9 only since the original patch didn't
> apply.
> 
> Commit faf37c44a105f3608115785f17cbbf3500f8bc71 upstream.

Thanks for this, and the 4.4 backport, both now queued up.

greg k-h