GRU Driver: TLB flushing, MMUOPS callouts

This file contains the functions for handlinf GRU TLB flushing, This
includes functions to handle the MMUOPS callouts.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/sgi-gru/grutlbpurge.c

+/*
+ * SN Platform GRU Driver
+ *
+ * 		MMUOPS callbacks  + TLB flushing
+ *
+ * This file handles emu notifier callbacks from the core kernel. The callbacks
+ * are used to update the TLB in the GRU as a result of changes in the
+ * state of a process address space. This file also handles TLB invalidates
+ * from the GRU driver.
+ *
+ *  Copyright (c) 2008 Silicon Graphics, Inc.  All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+ */
+
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/hugetlb.h>
+#include <linux/delay.h>
+#include <linux/timex.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+#include <asm/processor.h>
+#include "gru.h"
+#include "grutables.h"
+#include <asm/uv/uv_hub.h>
+
+#define gru_random()	get_cycles()
+
+/* ---------------------------------- TLB Invalidation functions --------
+ * get_tgh_handle
+ *
+ * Find a TGH to use for issuing a TLB invalidate. For GRUs that are on the
+ * local blade, use a fixed TGH that is a function of the blade-local cpu
+ * number. Normally, this TGH is private to the cpu & no contention occurs for
+ * the TGH. For offblade GRUs, select a random TGH in the range above the
+ * private TGHs. A spinlock is required to access this TGH & the lock must be
+ * released when the invalidate is completes. This sucks, but it is the best we
+ * can do.
+ *
+ * Note that the spinlock is IN the TGH handle so locking does not involve
+ * additional cache lines.
+ *
+ */
+static inline int get_off_blade_tgh(struct gru_state *gru)
+{
+	int n;
+
+	n = GRU_NUM_TGH - gru->gs_tgh_first_remote;
+	n = gru_random() % n;
+	n += gru->gs_tgh_first_remote;
+	return n;
+}
+
+static inline int get_on_blade_tgh(struct gru_state *gru)
+{
+	return uv_blade_processor_id() >> gru->gs_tgh_local_shift;
+}
+
+static struct gru_tlb_global_handle *get_lock_tgh_handle(struct gru_state
+							 *gru)
+{
+	struct gru_tlb_global_handle *tgh;
+	int n;
+
+	preempt_disable();
+	if (uv_numa_blade_id() == gru->gs_blade_id)
+		n = get_on_blade_tgh(gru);
+	else
+		n = get_off_blade_tgh(gru);
+	tgh = get_tgh_by_index(gru, n);
+	lock_tgh_handle(tgh);
+
+	return tgh;
+}
+
+static void get_unlock_tgh_handle(struct gru_tlb_global_handle *tgh)
+{
+	unlock_tgh_handle(tgh);
+	preempt_enable();
+}
+
+/*
+ * gru_flush_tlb_range
+ *
+ * General purpose TLB invalidation function. This function scans every GRU in
+ * the ENTIRE system (partition) looking for GRUs where the specified MM has
+ * been accessed by the GRU. For each GRU found, the TLB must be invalidated OR
+ * the ASID invalidated. Invalidating an ASID causes a new ASID to be assigned
+ * on the next fault. This effectively flushes the ENTIRE TLB for the MM at the
+ * cost of (possibly) a large number of future TLBmisses.
+ *
+ * The current algorithm is optimized based on the following (somewhat true)
+ * assumptions:
+ * 	- GRU contexts are not loaded into a GRU unless a reference is made to
+ * 	  the data segment or control block (this is true, not an assumption).
+ * 	  If a DS/CB is referenced, the user will also issue instructions that
+ * 	  cause TLBmisses. It is not necessary to optimize for the case where
+ * 	  contexts are loaded but no instructions cause TLB misses. (I know
+ * 	  this will happen but I'm not optimizing for it).
+ * 	- GRU instructions to invalidate TLB entries are SLOOOOWWW - normally
+ * 	  a few usec but in unusual cases, it could be longer. Avoid if
+ * 	  possible.
+ * 	- intrablade process migration between cpus is not frequent but is
+ * 	  common.
+ * 	- a GRU context is not typically migrated to a different GRU on the
+ * 	  blade because of intrablade migration
+ *	- interblade migration is rare. Processes migrate their GRU context to
+ *	  the new blade.
+ *	- if interblade migration occurs, migration back to the original blade
+ *	  is very very rare (ie., no optimization for this case)
+ *	- most GRU instruction operate on a subset of the user REGIONS. Code
+ *	  & shared library regions are not likely targets of GRU instructions.
+ *
+ * To help improve the efficiency of TLB invalidation, the GMS data
+ * structure is maintained for EACH address space (MM struct). The GMS is
+ * also the structure that contains the pointer to the mmu callout
+ * functions. This structure is linked to the mm_struct for the address space
+ * using the mmu "register" function. The mmu interfaces are used to
+ * provide the callbacks for TLB invalidation. The GMS contains:
+ *
+ * 	- asid[maxgrus] array. ASIDs are assigned to a GRU when a context is
+ * 	  loaded into the GRU.
+ * 	- asidmap[maxgrus]. bitmap to make it easier to find non-zero asids in
+ * 	  the above array
+ *	- ctxbitmap[maxgrus]. Indicates the contexts that are currently active
+ *	  in the GRU for the address space. This bitmap must be passed to the
+ *	  GRU to do an invalidate.
+ *
+ * The current algorithm for invalidating TLBs is:
+ * 	- scan the asidmap for GRUs where the context has been loaded, ie,
+ * 	  asid is non-zero.
+ * 	- for each gru found:
+ * 		- if the ctxtmap is non-zero, there are active contexts in the
+ * 		  GRU. TLB invalidate instructions must be issued to the GRU.
+ *		- if the ctxtmap is zero, no context is active. Set the ASID to
+ *		  zero to force a full TLB invalidation. This is fast but will
+ *		  cause a lot of TLB misses if the context is reloaded onto the
+ *		  GRU
+ *
+ */
+
+void gru_flush_tlb_range(struct gru_mm_struct *gms, unsigned long start,
+			 unsigned long len)
+{
+	struct gru_state *gru;
+	struct gru_mm_tracker *asids;
+	struct gru_tlb_global_handle *tgh;
+	unsigned long num;
+	int grupagesize, pagesize, pageshift, gid, asid;
+
+	/* ZZZ TODO - handle huge pages */
+	pageshift = PAGE_SHIFT;
+	pagesize = (1UL << pageshift);
+	grupagesize = GRU_PAGESIZE(pageshift);
+	num = min(((len + pagesize - 1) >> pageshift), GRUMAXINVAL);
+
+	STAT(flush_tlb);
+	gru_dbg(grudev, "gms %p, start 0x%lx, len 0x%lx, asidmap 0x%lx\n", gms,
+		start, len, gms->ms_asidmap[0]);
+
+	spin_lock(&gms->ms_asid_lock);
+	for_each_gru_in_bitmap(gid, gms->ms_asidmap) {
+		STAT(flush_tlb_gru);
+		gru = GID_TO_GRU(gid);
+		asids = gms->ms_asids + gid;
+		asid = asids->mt_asid;
+		if (asids->mt_ctxbitmap && asid) {
+			STAT(flush_tlb_gru_tgh);
+			asid = GRUASID(asid, start);
+			gru_dbg(grudev,
+	"  FLUSH gruid %d, asid 0x%x, num %ld, cbmap 0x%x\n",
+				gid, asid, num, asids->mt_ctxbitmap);
+			tgh = get_lock_tgh_handle(gru);
+			tgh_invalidate(tgh, start, 0, asid, grupagesize, 0,
+				       num - 1, asids->mt_ctxbitmap);
+			get_unlock_tgh_handle(tgh);
+		} else {
+			STAT(flush_tlb_gru_zero_asid);
+			asids->mt_asid = 0;
+			__clear_bit(gru->gs_gid, gms->ms_asidmap);
+			gru_dbg(grudev,
+	"  CLEARASID gruid %d, asid 0x%x, cbtmap 0x%x, asidmap 0x%lx\n",
+				gid, asid, asids->mt_ctxbitmap,
+				gms->ms_asidmap[0]);
+		}
+	}
+	spin_unlock(&gms->ms_asid_lock);
+}
+
+/*
+ * Flush the entire TLB on a chiplet.
+ */
+void gru_flush_all_tlb(struct gru_state *gru)
+{
+	struct gru_tlb_global_handle *tgh;
+
+	gru_dbg(grudev, "gru %p, gid %d\n", gru, gru->gs_gid);
+	tgh = get_lock_tgh_handle(gru);
+	tgh_invalidate(tgh, 0, ~0, 0, 1, 1, GRUMAXINVAL - 1, 0);
+	get_unlock_tgh_handle(tgh);
+	preempt_enable();
+}
+
+/*
+ * MMUOPS notifier callout functions
+ */
+static void gru_invalidate_range_start(struct mmu_notifier *mn,
+				       struct mm_struct *mm,
+				       unsigned long start, unsigned long end)
+{
+	struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
+						 ms_notifier);
+
+	STAT(mmu_invalidate_range);
+	atomic_inc(&gms->ms_range_active);
+	gru_dbg(grudev, "gms %p, start 0x%lx, end 0x%lx, act %d\n", gms,
+		start, end, atomic_read(&gms->ms_range_active));
+	gru_flush_tlb_range(gms, start, end - start);
+}
+
+static void gru_invalidate_range_end(struct mmu_notifier *mn,
+				     struct mm_struct *mm, unsigned long start,
+				     unsigned long end)
+{
+	struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
+						 ms_notifier);
+
+	atomic_dec(&gms->ms_range_active);
+	wake_up_all(&gms->ms_wait_queue);
+	gru_dbg(grudev, "gms %p, start 0x%lx, end 0x%lx\n", gms, start, end);
+}
+
+static void gru_invalidate_page(struct mmu_notifier *mn, struct mm_struct *mm,
+				unsigned long address)
+{
+	struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
+						 ms_notifier);
+
+	STAT(mmu_invalidate_page);
+	gru_flush_tlb_range(gms, address, PAGE_SIZE);
+	gru_dbg(grudev, "gms %p, address 0x%lx\n", gms, address);
+}
+
+static void gru_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
+						 ms_notifier);
+
+	gms->ms_released = 1;
+	gru_dbg(grudev, "gms %p\n", gms);
+}
+
+
+static const struct mmu_notifier_ops gru_mmuops = {
+	.invalidate_page	= gru_invalidate_page,
+	.invalidate_range_start	= gru_invalidate_range_start,
+	.invalidate_range_end	= gru_invalidate_range_end,
+	.release		= gru_release,
+};
+
+/* Move this to the basic mmu_notifier file. But for now... */
+static struct mmu_notifier *mmu_find_ops(struct mm_struct *mm,
+			const struct mmu_notifier_ops *ops)
+{
+	struct mmu_notifier *mn, *gru_mn = NULL;
+	struct hlist_node *n;
+
+	if (mm->mmu_notifier_mm) {
+		rcu_read_lock();
+		hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list,
+					 hlist)
+		    if (mn->ops == ops) {
+			gru_mn = mn;
+			break;
+		}
+		rcu_read_unlock();
+	}
+	return gru_mn;
+}
+
+struct gru_mm_struct *gru_register_mmu_notifier(void)
+{
+	struct gru_mm_struct *gms;
+	struct mmu_notifier *mn;
+
+	mn = mmu_find_ops(current->mm, &gru_mmuops);
+	if (mn) {
+		gms = container_of(mn, struct gru_mm_struct, ms_notifier);
+		atomic_inc(&gms->ms_refcnt);
+	} else {
+		gms = kzalloc(sizeof(*gms), GFP_KERNEL);
+		if (gms) {
+			spin_lock_init(&gms->ms_asid_lock);
+			gms->ms_notifier.ops = &gru_mmuops;
+			atomic_set(&gms->ms_refcnt, 1);
+			init_waitqueue_head(&gms->ms_wait_queue);
+			__mmu_notifier_register(&gms->ms_notifier, current->mm);
+		}
+	}
+	gru_dbg(grudev, "gms %p, refcnt %d\n", gms,
+		atomic_read(&gms->ms_refcnt));
+	return gms;
+}
+
+void gru_drop_mmu_notifier(struct gru_mm_struct *gms)
+{
+	gru_dbg(grudev, "gms %p, refcnt %d, released %d\n", gms,
+		atomic_read(&gms->ms_refcnt), gms->ms_released);
+	if (atomic_dec_return(&gms->ms_refcnt) == 0) {
+		if (!gms->ms_released)
+			mmu_notifier_unregister(&gms->ms_notifier, current->mm);
+		kfree(gms);
+	}
+}
+
+/*
+ * Setup TGH parameters. There are:
+ * 	- 24 TGH handles per GRU chiplet
+ * 	- a portion (MAX_LOCAL_TGH) of the handles are reserved for
+ * 	  use by blade-local cpus
+ * 	- the rest are used by off-blade cpus. This usage is
+ * 	  less frequent than blade-local usage.
+ *
+ * For now, use 16 handles for local flushes, 8 for remote flushes. If the blade
+ * has less tan or equal to 16 cpus, each cpu has a unique handle that it can
+ * use.
+ */
+#define MAX_LOCAL_TGH	16
+
+void gru_tgh_flush_init(struct gru_state *gru)
+{
+	int cpus, shift = 0, n;
+
+	cpus = uv_blade_nr_possible_cpus(gru->gs_blade_id);
+
+	/* n = cpus rounded up to next power of 2 */
+	if (cpus) {
+		n = 1 << fls(cpus - 1);
+
+		/*
+		 * shift count for converting local cpu# to TGH index
+		 *      0 if cpus <= MAX_LOCAL_TGH,
+		 *      1 if cpus <= 2*MAX_LOCAL_TGH,
+		 *      etc
+		 */
+		shift = max(0, fls(n - 1) - fls(MAX_LOCAL_TGH - 1));
+	}
+	gru->gs_tgh_local_shift = shift;
+
+	/* first starting TGH index to use for remote purges */
+	gru->gs_tgh_first_remote = (cpus + (1 << shift) - 1) >> shift;
+
+}