powerpc/64s: Clear PCR on boot

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
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

2 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/cpu_setup_power.S b/arch/powerpc/kernel/cpu_setup_power.S
index 3f30c994e931..458b928dbd84 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
         li      r4,(LPCR_LPES1 >> LPCR_LPES_SH)
         bl      __init_LPCR_ISA206
@@ -41,6 +42,7 @@ _GLOBAL(__restore_cpu_power7)
         beqlr
         li      r0,0
         mtspr   SPRN_LPID,r0
+        mtspr   SPRN_PCR,r0
         mfspr   r3,SPRN_LPCR
         li      r4,(LPCR_LPES1 >> LPCR_LPES_SH)
         bl      __init_LPCR_ISA206
@@ -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
         li      r4,0 /* LPES = 0 */
@@ -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
         li      r4,0 /* LPES = 0 */
@@ -99,6 +103,7 @@ _GLOBAL(__setup_cpu_power9)
         mtspr   SPRN_PSSCR,r0
         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  | LPCR_HEIC)
         or      r3, r3, r4
@@ -123,6 +128,7 @@ _GLOBAL(__restore_cpu_power9)
         mtspr   SPRN_PSSCR,r0
         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 | LPCR_HEIC)
         or      r3, r3, r4
diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index 8ab51f6ca03a..c904477abaf3 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -101,6 +101,7 @@ static void __restore_cpu_cpufeatures(void)
         if (hv_mode) {
                 mtspr(SPRN_LPID, 0);
                 mtspr(SPRN_HFSCR, system_registers.hfscr);
+                mtspr(SPRN_PCR, 0);
         }
         mtspr(SPRN_FSCR, system_registers.fscr);