csky: Add new asid lib code from arm

This patch only contains asid help code from arm for next patch to
use.

The asid allocator use five level check to reduce the cost of
switch_mm.

 1. Check if the asid version is the same (it's general)
 2. Check reserved_asid which is set in rollover flush_context()
    and key point is to keep the same bit position with the current
    asid version instead of input version.
 3. Check if the position of bitmap is free then it could be set &
    used directly.
 4. find_next_zero_bit() (a little performance cost)
 5. flush_context  (this is the worst cost with increase current asid
    version)

Check is level by level and cost is also higher with the next level.
The reserved_asid and bitmap mechanism prevent unnecessary
find_next_zero_bit().

The atomic 64 bit asid is also suitable for 32-bit system and it
won't cost a lot in 1th 2th 3th level check.

The operation of set/clear mm_cpumask was removed in arm64 compared to
arm32. It seems no side effect on current arm64 system, but from
software meaning it's wrong. Although csky also needn't it, we add it
back for csky.

The asid_per_ctxt is no use for csky and it reserves the lowest bits for
other use, maybe: trust zone ? Ok, just keep it in csky copy.

Seems it also could be used by other archs and it's worth to move asid
code to generic in future.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Julien Grall <julien.grall@arm.com>

arch/csky/include/asm/asid.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ASM_ASID_H
+#define __ASM_ASM_ASID_H
+
+#include <linux/atomic.h>
+#include <linux/compiler.h>
+#include <linux/cpumask.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+
+struct asid_info
+{
+	atomic64_t	generation;
+	unsigned long	*map;
+	atomic64_t __percpu	*active;
+	u64 __percpu		*reserved;
+	u32			bits;
+	/* Lock protecting the structure */
+	raw_spinlock_t		lock;
+	/* Which CPU requires context flush on next call */
+	cpumask_t		flush_pending;
+	/* Number of ASID allocated by context (shift value) */
+	unsigned int		ctxt_shift;
+	/* Callback to locally flush the context. */
+	void			(*flush_cpu_ctxt_cb)(void);
+};
+
+#define NUM_ASIDS(info)			(1UL << ((info)->bits))
+#define NUM_CTXT_ASIDS(info)		(NUM_ASIDS(info) >> (info)->ctxt_shift)
+
+#define active_asid(info, cpu)	*per_cpu_ptr((info)->active, cpu)
+
+void asid_new_context(struct asid_info *info, atomic64_t *pasid,
+		      unsigned int cpu, struct mm_struct *mm);
+
+/*
+ * Check the ASID is still valid for the context. If not generate a new ASID.
+ *
+ * @pasid: Pointer to the current ASID batch
+ * @cpu: current CPU ID. Must have been acquired throught get_cpu()
+ */
+static inline void asid_check_context(struct asid_info *info,
+				      atomic64_t *pasid, unsigned int cpu,
+				      struct mm_struct *mm)
+{
+	u64 asid, old_active_asid;
+
+	asid = atomic64_read(pasid);
+
+	/*
+	 * The memory ordering here is subtle.
+	 * If our active_asid is non-zero and the ASID matches the current
+	 * generation, then we update the active_asid entry with a relaxed
+	 * cmpxchg. Racing with a concurrent rollover means that either:
+	 *
+	 * - We get a zero back from the cmpxchg and end up waiting on the
+	 *   lock. Taking the lock synchronises with the rollover and so
+	 *   we are forced to see the updated generation.
+	 *
+	 * - We get a valid ASID back from the cmpxchg, which means the
+	 *   relaxed xchg in flush_context will treat us as reserved
+	 *   because atomic RmWs are totally ordered for a given location.
+	 */
+	old_active_asid = atomic64_read(&active_asid(info, cpu));
+	if (old_active_asid &&
+	    !((asid ^ atomic64_read(&info->generation)) >> info->bits) &&
+	    atomic64_cmpxchg_relaxed(&active_asid(info, cpu),
+				     old_active_asid, asid))
+		return;
+
+	asid_new_context(info, pasid, cpu, mm);
+}
+
+int asid_allocator_init(struct asid_info *info,
+			u32 bits, unsigned int asid_per_ctxt,
+			void (*flush_cpu_ctxt_cb)(void));
+
+#endif

arch/csky/mm/Makefile

@@ -12,3 +12,4 @@ obj-y +=			init.o
 obj-y +=			ioremap.o
 obj-y +=			syscache.o
 obj-y +=			tlb.o
+obj-y +=			asid.o

arch/csky/mm/asid.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic ASID allocator.
+ *
+ * Based on arch/arm/mm/context.c
+ *
+ * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
+ * Copyright (C) 2012 ARM Ltd.
+ */
+
+#include <linux/slab.h>
+#include <linux/mm_types.h>
+
+#include <asm/asid.h>
+
+#define reserved_asid(info, cpu) *per_cpu_ptr((info)->reserved, cpu)
+
+#define ASID_MASK(info)			(~GENMASK((info)->bits - 1, 0))
+#define ASID_FIRST_VERSION(info)	(1UL << ((info)->bits))
+
+#define asid2idx(info, asid)		(((asid) & ~ASID_MASK(info)) >> (info)->ctxt_shift)
+#define idx2asid(info, idx)		(((idx) << (info)->ctxt_shift) & ~ASID_MASK(info))
+
+static void flush_context(struct asid_info *info)
+{
+	int i;
+	u64 asid;
+
+	/* Update the list of reserved ASIDs and the ASID bitmap. */
+	bitmap_clear(info->map, 0, NUM_CTXT_ASIDS(info));
+
+	for_each_possible_cpu(i) {
+		asid = atomic64_xchg_relaxed(&active_asid(info, i), 0);
+		/*
+		 * If this CPU has already been through a
+		 * rollover, but hasn't run another task in
+		 * the meantime, we must preserve its reserved
+		 * ASID, as this is the only trace we have of
+		 * the process it is still running.
+		 */
+		if (asid == 0)
+			asid = reserved_asid(info, i);
+		__set_bit(asid2idx(info, asid), info->map);
+		reserved_asid(info, i) = asid;
+	}
+
+	/*
+	 * Queue a TLB invalidation for each CPU to perform on next
+	 * context-switch
+	 */
+	cpumask_setall(&info->flush_pending);
+}
+
+static bool check_update_reserved_asid(struct asid_info *info, u64 asid,
+				       u64 newasid)
+{
+	int cpu;
+	bool hit = false;
+
+	/*
+	 * Iterate over the set of reserved ASIDs looking for a match.
+	 * If we find one, then we can update our mm to use newasid
+	 * (i.e. the same ASID in the current generation) but we can't
+	 * exit the loop early, since we need to ensure that all copies
+	 * of the old ASID are updated to reflect the mm. Failure to do
+	 * so could result in us missing the reserved ASID in a future
+	 * generation.
+	 */
+	for_each_possible_cpu(cpu) {
+		if (reserved_asid(info, cpu) == asid) {
+			hit = true;
+			reserved_asid(info, cpu) = newasid;
+		}
+	}
+
+	return hit;
+}
+
+static u64 new_context(struct asid_info *info, atomic64_t *pasid,
+		       struct mm_struct *mm)
+{
+	static u32 cur_idx = 1;
+	u64 asid = atomic64_read(pasid);
+	u64 generation = atomic64_read(&info->generation);
+
+	if (asid != 0) {
+		u64 newasid = generation | (asid & ~ASID_MASK(info));
+
+		/*
+		 * If our current ASID was active during a rollover, we
+		 * can continue to use it and this was just a false alarm.
+		 */
+		if (check_update_reserved_asid(info, asid, newasid))
+			return newasid;
+
+		/*
+		 * We had a valid ASID in a previous life, so try to re-use
+		 * it if possible.
+		 */
+		if (!__test_and_set_bit(asid2idx(info, asid), info->map))
+			return newasid;
+	}
+
+	/*
+	 * Allocate a free ASID. If we can't find one, take a note of the
+	 * currently active ASIDs and mark the TLBs as requiring flushes.  We
+	 * always count from ASID #2 (index 1), as we use ASID #0 when setting
+	 * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
+	 * pairs.
+	 */
+	asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), cur_idx);
+	if (asid != NUM_CTXT_ASIDS(info))
+		goto set_asid;
+
+	/* We're out of ASIDs, so increment the global generation count */
+	generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION(info),
+						 &info->generation);
+	flush_context(info);
+
+	/* We have more ASIDs than CPUs, so this will always succeed */
+	asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), 1);
+
+set_asid:
+	__set_bit(asid, info->map);
+	cur_idx = asid;
+	cpumask_clear(mm_cpumask(mm));
+	return idx2asid(info, asid) | generation;
+}
+
+/*
+ * Generate a new ASID for the context.
+ *
+ * @pasid: Pointer to the current ASID batch allocated. It will be updated
+ * with the new ASID batch.
+ * @cpu: current CPU ID. Must have been acquired through get_cpu()
+ */
+void asid_new_context(struct asid_info *info, atomic64_t *pasid,
+		      unsigned int cpu, struct mm_struct *mm)
+{
+	unsigned long flags;
+	u64 asid;
+
+	raw_spin_lock_irqsave(&info->lock, flags);
+	/* Check that our ASID belongs to the current generation. */
+	asid = atomic64_read(pasid);
+	if ((asid ^ atomic64_read(&info->generation)) >> info->bits) {
+		asid = new_context(info, pasid, mm);
+		atomic64_set(pasid, asid);
+	}
+
+	if (cpumask_test_and_clear_cpu(cpu, &info->flush_pending))
+		info->flush_cpu_ctxt_cb();
+
+	atomic64_set(&active_asid(info, cpu), asid);
+	cpumask_set_cpu(cpu, mm_cpumask(mm));
+	raw_spin_unlock_irqrestore(&info->lock, flags);
+}
+
+/*
+ * Initialize the ASID allocator
+ *
+ * @info: Pointer to the asid allocator structure
+ * @bits: Number of ASIDs available
+ * @asid_per_ctxt: Number of ASIDs to allocate per-context. ASIDs are
+ * allocated contiguously for a given context. This value should be a power of
+ * 2.
+ */
+int asid_allocator_init(struct asid_info *info,
+			u32 bits, unsigned int asid_per_ctxt,
+			void (*flush_cpu_ctxt_cb)(void))
+{
+	info->bits = bits;
+	info->ctxt_shift = ilog2(asid_per_ctxt);
+	info->flush_cpu_ctxt_cb = flush_cpu_ctxt_cb;
+	/*
+	 * Expect allocation after rollover to fail if we don't have at least
+	 * one more ASID than CPUs. ASID #0 is always reserved.
+	 */
+	WARN_ON(NUM_CTXT_ASIDS(info) - 1 <= num_possible_cpus());
+	atomic64_set(&info->generation, ASID_FIRST_VERSION(info));
+	info->map = kcalloc(BITS_TO_LONGS(NUM_CTXT_ASIDS(info)),
+			    sizeof(*info->map), GFP_KERNEL);
+	if (!info->map)
+		return -ENOMEM;
+
+	raw_spin_lock_init(&info->lock);
+
+	return 0;
+}