powerpc/64s/radix: introduce options to disable use of the tlbie instruction

Introduce two options to control the use of the tlbie instruction. A
boot time option which completely disables the kernel using the
instruction, this is currently incompatible with HASH MMU, KVM, and
coherent accelerators.

And a debugfs option can be switched at runtime and avoids using tlbie
for invalidating CPU TLBs for normal process and kernel address
mappings. Coherent accelerators are still managed with tlbie, as will
KVM partition scope translations.

Cross-CPU TLB flushing is implemented with IPIs and tlbiel. This is a
basic implementation which does not attempt to make any optimisation
beyond the tlbie implementation.

This is useful for performance testing among other things. For example
in certain situations on large systems, using IPIs may be faster than
tlbie as they can be directed rather than broadcast. Later we may also
take advantage of the IPIs to do more interesting things such as trim
the mm cpumask more aggressively.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190902152931.17840-7-npiggin@gmail.com

arch/powerpc/mm/book3s64/pgtable.c

@@ -8,6 +8,7 @@
 #include <linux/memblock.h>
 #include <misc/cxl-base.h>
 
+#include <asm/debugfs.h>
 #include <asm/pgalloc.h>
 #include <asm/tlb.h>
 #include <asm/trace.h>
@@ -469,3 +470,49 @@ int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
 
 	return true;
 }
+
+/*
+ * Does the CPU support tlbie?
+ */
+bool tlbie_capable __read_mostly = true;
+EXPORT_SYMBOL(tlbie_capable);
+
+/*
+ * Should tlbie be used for management of CPU TLBs, for kernel and process
+ * address spaces? tlbie may still be used for nMMU accelerators, and for KVM
+ * guest address spaces.
+ */
+bool tlbie_enabled __read_mostly = true;
+
+static int __init setup_disable_tlbie(char *str)
+{
+	if (!radix_enabled()) {
+		pr_err("disable_tlbie: Unable to disable TLBIE with Hash MMU.\n");
+		return 1;
+	}
+
+	tlbie_capable = false;
+	tlbie_enabled = false;
+
+        return 1;
+}
+__setup("disable_tlbie", setup_disable_tlbie);
+
+static int __init pgtable_debugfs_setup(void)
+{
+	if (!tlbie_capable)
+		return 0;
+
+	/*
+	 * There is no locking vs tlb flushing when changing this value.
+	 * The tlb flushers will see one value or another, and use either
+	 * tlbie or tlbiel with IPIs. In both cases the TLBs will be
+	 * invalidated as expected.
+	 */
+	debugfs_create_bool("tlbie_enabled", 0600,
+			powerpc_debugfs_root,
+			&tlbie_enabled);
+
+	return 0;
+}
+arch_initcall(pgtable_debugfs_setup);