arm64: Process management

The patch adds support for thread creation and context switching. The
context switching CPU specific code is introduced with the CPU support
patch (part of the arch/arm64/mm/proc.S file). AArch64 supports
ASID-tagged TLBs and the ASID can be either 8 or 16-bit wide (detectable
via the ID_AA64AFR0_EL1 register).

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 159 insertions, 0 deletions

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
new file mode 100644
index 0000000..baa758d
--- /dev/null
+++ b/arch/arm64/mm/context.c
@@ -0,0 +1,159 @@
+/*
+ * Based on arch/arm/mm/context.c
+ *
+ * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/percpu.h>
+
+#include <asm/mmu_context.h>
+#include <asm/tlbflush.h>
+#include <asm/cachetype.h>
+
+#define asid_bits(reg) \
+	(((read_cpuid(ID_AA64MMFR0_EL1) & 0xf0) >> 2) + 8)
+
+#define ASID_FIRST_VERSION	(1 << MAX_ASID_BITS)
+
+static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
+unsigned int cpu_last_asid = ASID_FIRST_VERSION;
+
+/*
+ * We fork()ed a process, and we need a new context for the child to run in.
+ */
+void __init_new_context(struct task_struct *tsk, struct mm_struct *mm)
+{
+	mm->context.id = 0;
+	raw_spin_lock_init(&mm->context.id_lock);
+}
+
+static void flush_context(void)
+{
+	/* set the reserved TTBR0 before flushing the TLB */
+	cpu_set_reserved_ttbr0();
+	flush_tlb_all();
+	if (icache_is_aivivt())
+		__flush_icache_all();
+}
+
+#ifdef CONFIG_SMP
+
+static void set_mm_context(struct mm_struct *mm, unsigned int asid)
+{
+	unsigned long flags;
+
+	/*
+	 * Locking needed for multi-threaded applications where the same
+	 * mm->context.id could be set from different CPUs during the
+	 * broadcast. This function is also called via IPI so the
+	 * mm->context.id_lock has to be IRQ-safe.
+	 */
+	raw_spin_lock_irqsave(&mm->context.id_lock, flags);
+	if (likely((mm->context.id ^ cpu_last_asid) >> MAX_ASID_BITS)) {
+		/*
+		 * Old version of ASID found. Set the new one and reset
+		 * mm_cpumask(mm).
+		 */
+		mm->context.id = asid;
+		cpumask_clear(mm_cpumask(mm));
+	}
+	raw_spin_unlock_irqrestore(&mm->context.id_lock, flags);
+
+	/*
+	 * Set the mm_cpumask(mm) bit for the current CPU.
+	 */
+	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
+}
+
+/*
+ * Reset the ASID on the current CPU. This function call is broadcast from the
+ * CPU handling the ASID rollover and holding cpu_asid_lock.
+ */
+static void reset_context(void *info)
+{
+	unsigned int asid;
+	unsigned int cpu = smp_processor_id();
+	struct mm_struct *mm = current->active_mm;
+
+	smp_rmb();
+	asid = cpu_last_asid + cpu;
+
+	flush_context();
+	set_mm_context(mm, asid);
+
+	/* set the new ASID */
+	cpu_switch_mm(mm->pgd, mm);
+}
+
+#else
+
+static inline void set_mm_context(struct mm_struct *mm, unsigned int asid)
+{
+	mm->context.id = asid;
+	cpumask_copy(mm_cpumask(mm), cpumask_of(smp_processor_id()));
+}
+
+#endif
+
+void __new_context(struct mm_struct *mm)
+{
+	unsigned int asid;
+	unsigned int bits = asid_bits();
+
+	raw_spin_lock(&cpu_asid_lock);
+#ifdef CONFIG_SMP
+	/*
+	 * Check the ASID again, in case the change was broadcast from another
+	 * CPU before we acquired the lock.
+	 */
+	if (!unlikely((mm->context.id ^ cpu_last_asid) >> MAX_ASID_BITS)) {
+		cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
+		raw_spin_unlock(&cpu_asid_lock);
+		return;
+	}
+#endif
+	/*
+	 * At this point, it is guaranteed that the current mm (with an old
+	 * ASID) isn't active on any other CPU since the ASIDs are changed
+	 * simultaneously via IPI.
+	 */
+	asid = ++cpu_last_asid;
+
+	/*
+	 * If we've used up all our ASIDs, we need to start a new version and
+	 * flush the TLB.
+	 */
+	if (unlikely((asid & ((1 << bits) - 1)) == 0)) {
+		/* increment the ASID version */
+		cpu_last_asid += (1 << MAX_ASID_BITS) - (1 << bits);
+		if (cpu_last_asid == 0)
+			cpu_last_asid = ASID_FIRST_VERSION;
+		asid = cpu_last_asid + smp_processor_id();
+		flush_context();
+#ifdef CONFIG_SMP
+		smp_wmb();
+		smp_call_function(reset_context, NULL, 1);
+#endif
+		cpu_last_asid += NR_CPUS - 1;
+	}
+
+	set_mm_context(mm, asid);
+	raw_spin_unlock(&cpu_asid_lock);
+}