MIPS: 64-bit: Detect virtual memory size

Linux kernel 2.6.32 and later allocate address space from the top of the
kernel virtual memory address space.

This patch implements virtual memory size detection for 64 bit MIPS CPUs
to avoid resulting crashes.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/935/
Reviewed-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/cpu-probe.c

@@ -284,6 +284,15 @@ static inline int __cpu_has_fpu(void)
 	return ((cpu_get_fpu_id() & 0xff00) != FPIR_IMP_NONE);
 }
 
+static inline void cpu_probe_vmbits(struct cpuinfo_mips *c)
+{
+#ifdef __NEED_VMBITS_PROBE
+	write_c0_entryhi(0x3ffffffffffff000ULL);
+	back_to_back_c0_hazard();
+	c->vmbits = fls64(read_c0_entryhi() & 0x3ffffffffffff000ULL);
+#endif
+}
+
 #define R4K_OPTS (MIPS_CPU_TLB | MIPS_CPU_4KEX | MIPS_CPU_4K_CACHE \
 		| MIPS_CPU_COUNTER)
 
@@ -969,6 +978,8 @@ __cpuinit void cpu_probe(void)
 		c->srsets = ((read_c0_srsctl() >> 26) & 0x0f) + 1;
 	else
 		c->srsets = 1;
+
+	cpu_probe_vmbits(c);
 }
 
 __cpuinit void cpu_report(void)