powerpc/64s: Clear PCR on boot

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@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[bwh: Backported to 3.16: Drop changes in __{setup,restore}_cpu_power9
 and __restore_cpu_cpufeatures()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/powerpc/kernel/cpu_setup_power.S b/arch/powerpc/kernel/cpu_setup_power.S
index 46733535cc0b482a1ea35fe8411c556fb26fcb3b..4fadf576ec46d4b72cbab972bd923ade6bae10cd 100644 (file)
--- 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