powerpc/pseries: Add support for hash table resizing

This adds support for using two hypercalls to change the size of the
main hash page table while running as a PAPR guest. For now these
hypercalls are only in experimental qemu versions.

The interface is two part: first H_RESIZE_HPT_PREPARE is used to
allocate and prepare the new hash table. This may be slow, but can be
done asynchronously. Then, H_RESIZE_HPT_COMMIT is used to switch to the
new hash table. This requires that no CPUs be concurrently updating the
HPT, and so must be run under stop_machine().

This also adds a debugfs file which can be used to manually control
HPT resizing or testing purposes.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Paul Mackerras <paulus@samba.org>
[mpe: Rename the debugfs file to "hpt_order"]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 67e19a0821be..a3371d4e35b6 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -35,7 +35,9 @@
 #include <linux/memblock.h>
 #include <linux/context_tracking.h>
 #include <linux/libfdt.h>
+#include <linux/debugfs.h>
 
+#include <asm/debug.h>
 #include <asm/processor.h>
 #include <asm/pgtable.h>
 #include <asm/mmu.h>
@@ -1795,3 +1797,34 @@ void hash__setup_initial_memory_limit(phys_addr_t first_memblock_base,
 	/* Finally limit subsequent allocations */
 	memblock_set_current_limit(ppc64_rma_size);
 }
+
+#ifdef CONFIG_DEBUG_FS
+
+static int hpt_order_get(void *data, u64 *val)
+{
+	*val = ppc64_pft_size;
+	return 0;
+}
+
+static int hpt_order_set(void *data, u64 val)
+{
+	if (!mmu_hash_ops.resize_hpt)
+		return -ENODEV;
+
+	return mmu_hash_ops.resize_hpt(val);
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_hpt_order, hpt_order_get, hpt_order_set, "%llu\n");
+
+static int __init hash64_debugfs(void)
+{
+	if (!debugfs_create_file("hpt_order", 0600, powerpc_debugfs_root,
+				 NULL, &fops_hpt_order)) {
+		pr_err("lpar: unable to create hpt_order debugsfs file\n");
+	}
+
+	return 0;
+}
+machine_device_initcall(pseries, hash64_debugfs);
+
+#endif /* CONFIG_DEBUG_FS */