powerpc: In HV mode, use HSPRG0 for PACA

When running in Hypervisor mode (arch 2.06 or later), we store the PACA
in HSPRG0 instead of SPRG1. The architecture specifies that SPRGs may be
lost during a "nap" power management operation (though they aren't
currently on POWER7) and this enables use of SPRG1 by KVM guests.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/paca.c

@@ -156,11 +156,22 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
 /* Put the paca pointer into r13 and SPRG_PACA */
 void setup_paca(struct paca_struct *new_paca)
 {
+	/* Setup r13 */
 	local_paca = new_paca;
-	mtspr(SPRN_SPRG_PACA, local_paca);
+
 #ifdef CONFIG_PPC_BOOK3E
+	/* On Book3E, initialize the TLB miss exception frames */
 	mtspr(SPRN_SPRG_TLB_EXFRAME, local_paca->extlb);
+#else
+	/* In HV mode, we setup both HPACA and PACA to avoid problems
+	 * if we do a GET_PACA() before the feature fixups have been
+	 * applied
+	 */
+	if (cpu_has_feature(CPU_FTR_HVMODE_206))
+		mtspr(SPRN_SPRG_HPACA, local_paca);
 #endif
+	mtspr(SPRN_SPRG_PACA, local_paca);
+
 }
 
 static int __initdata paca_size;