sh: hw-breakpoints: Add preliminary support for SH-4A UBC.

This adds preliminary support for the SH-4A UBC to the hw-breakpoints API.
Presently only a single channel is implemented, and the ptrace interface
still needs to be converted. This is the first step to cleaning up the
long-standing UBC mess, making the UBC more generally accessible, and
finally making it SMP safe.

An additional abstraction will be layered on top of this as with the perf
events code to permit the various CPU families to wire up support for
their own specific UBCs, as many variations exist.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 416 insertions, 0 deletions

diff --git a/arch/sh/kernel/hw_breakpoint.c b/arch/sh/kernel/hw_breakpoint.c
new file mode 100644
index 000000000000..ff3cb3d7df8f
--- /dev/null
+++ b/arch/sh/kernel/hw_breakpoint.c
@@ -0,0 +1,416 @@
+/*
+ * arch/sh/kernel/hw_breakpoint.c
+ *
+ * Unified kernel/user-space hardware breakpoint facility for the on-chip UBC.
+ *
+ * Copyright (C) 2009  Paul Mundt
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+#include <linux/init.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/percpu.h>
+#include <linux/kallsyms.h>
+#include <linux/notifier.h>
+#include <linux/kprobes.h>
+#include <linux/kdebug.h>
+#include <linux/io.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/mmu_context.h>
+
+struct ubc_context {
+	unsigned long pc;
+	unsigned long state;
+};
+
+/* Per cpu ubc channel state */
+static DEFINE_PER_CPU(struct ubc_context, ubc_ctx[HBP_NUM]);
+
+/*
+ * Stores the breakpoints currently in use on each breakpoint address
+ * register for each cpus
+ */
+static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
+
+static int __init ubc_init(void)
+{
+	__raw_writel(0, UBC_CAMR0);
+	__raw_writel(0, UBC_CBR0);
+	__raw_writel(0, UBC_CBCR);
+
+	__raw_writel(UBC_CRR_BIE | UBC_CRR_PCB, UBC_CRR0);
+
+	/* dummy read for write posting */
+	(void)__raw_readl(UBC_CRR0);
+
+	return 0;
+}
+arch_initcall(ubc_init);
+
+/*
+ * Install a perf counter breakpoint.
+ *
+ * We seek a free UBC channel and use it for this breakpoint.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct ubc_context *ubc_ctx;
+	int i;
+
+	for (i = 0; i < HBP_NUM; i++) {
+		struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
+		return -EBUSY;
+
+	ubc_ctx = &__get_cpu_var(ubc_ctx[i]);
+
+	ubc_ctx->pc = info->address;
+	ubc_ctx->state = info->len | info->type;
+
+	__raw_writel(UBC_CBR_CE | ubc_ctx->state, UBC_CBR0);
+	__raw_writel(ubc_ctx->pc, UBC_CAR0);
+
+	return 0;
+}
+
+/*
+ * Uninstall the breakpoint contained in the given counter.
+ *
+ * First we search the debug address register it uses and then we disable
+ * it.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct ubc_context *ubc_ctx;
+	int i;
+
+	for (i = 0; i < HBP_NUM; i++) {
+		struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
+		return;
+
+	ubc_ctx = &__get_cpu_var(ubc_ctx[i]);
+	ubc_ctx->pc = 0;
+	ubc_ctx->state &= ~(info->len | info->type);
+
+	__raw_writel(ubc_ctx->pc, UBC_CBR0);
+	__raw_writel(ubc_ctx->state, UBC_CAR0);
+}
+
+static int get_hbp_len(u16 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case SH_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case SH_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case SH_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case SH_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+	return len_in_bytes;
+}
+
+/*
+ * Check for virtual address in user space.
+ */
+int arch_check_va_in_userspace(unsigned long va, u16 hbp_len)
+{
+	unsigned int len;
+
+	len = get_hbp_len(hbp_len);
+
+	return (va <= TASK_SIZE - len);
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+static int arch_check_va_in_kernelspace(unsigned long va, u8 hbp_len)
+{
+	unsigned int len;
+
+	len = get_hbp_len(hbp_len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Store a breakpoint's encoded address, length, and type.
+ */
+static int arch_store_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/*
+	 * User-space requests will always have the address field populated
+	 * For kernel-addresses, either the address or symbol name can be
+	 * specified.
+	 */
+	if (info->name)
+		info->address = (unsigned long)kallsyms_lookup_name(info->name);
+	if (info->address) {
+		info->asid = get_asid();
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+int arch_bp_generic_fields(int sh_len, int sh_type,
+			   int *gen_len, int *gen_type)
+{
+	/* Len */
+	switch (sh_len) {
+	case SH_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case SH_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case SH_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case SH_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Type */
+	switch (sh_type) {
+	case SH_BREAKPOINT_READ:
+		*gen_type = HW_BREAKPOINT_R;
+	case SH_BREAKPOINT_WRITE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case SH_BREAKPOINT_RW:
+		*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	info->address = bp->attr.bp_addr;
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->len = SH_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->len = SH_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->len = SH_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->len = SH_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_R:
+		info->type = SH_BREAKPOINT_READ;
+		break;
+	case HW_BREAKPOINT_W:
+		info->type = SH_BREAKPOINT_WRITE;
+		break;
+	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
+		info->type = SH_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp,
+				  struct task_struct *tsk)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	unsigned int align;
+	int ret;
+
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		return ret;
+
+	ret = -EINVAL;
+
+	switch (info->len) {
+	case SH_BREAKPOINT_LEN_1:
+		align = 0;
+		break;
+	case SH_BREAKPOINT_LEN_2:
+		align = 1;
+		break;
+	case SH_BREAKPOINT_LEN_4:
+		align = 3;
+		break;
+	case SH_BREAKPOINT_LEN_8:
+		align = 7;
+		break;
+	default:
+		return ret;
+	}
+
+	if (bp->callback)
+		ret = arch_store_info(bp);
+
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Check that the low-order bits of the address are appropriate
+	 * for the alignment implied by len.
+	 */
+	if (info->address & align)
+		return -EINVAL;
+
+	/* Check that the virtual address is in the proper range */
+	if (tsk) {
+		if (!arch_check_va_in_userspace(info->address, info->len))
+			return -EFAULT;
+	} else {
+		if (!arch_check_va_in_kernelspace(info->address, info->len))
+			return -EFAULT;
+	}
+
+	return 0;
+}
+
+/*
+ * Release the user breakpoints used by ptrace
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+	int i;
+	struct thread_struct *t = &tsk->thread;
+
+	for (i = 0; i < HBP_NUM; i++) {
+		unregister_hw_breakpoint(t->ptrace_bps[i]);
+		t->ptrace_bps[i] = NULL;
+	}
+}
+
+static int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+	int cpu, i, rc = NOTIFY_STOP;
+	struct perf_event *bp;
+	unsigned long val;
+
+	val = __raw_readl(UBC_CBR0);
+	__raw_writel(val & ~UBC_CBR_CE, UBC_CBR0);
+
+	cpu = get_cpu();
+	for (i = 0; i < HBP_NUM; i++) {
+		/*
+		 * The counter may be concurrently released but that can only
+		 * occur from a call_rcu() path. We can then safely fetch
+		 * the breakpoint, use its callback, touch its counter
+		 * while we are in an rcu_read_lock() path.
+		 */
+		rcu_read_lock();
+
+		bp = per_cpu(bp_per_reg[i], cpu);
+		if (bp) {
+			rc = NOTIFY_DONE;
+		} else {
+			rcu_read_unlock();
+			break;
+		}
+
+		(bp->callback)(bp, args->regs);
+
+		rcu_read_unlock();
+	}
+
+	if (bp) {
+		struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+		__raw_writel(UBC_CBR_CE | info->len | info->type, UBC_CBR0);
+		__raw_writel(info->address, UBC_CAR0);
+	}
+
+	put_cpu();
+
+	return rc;
+}
+
+BUILD_TRAP_HANDLER(breakpoint)
+{
+	unsigned long ex = lookup_exception_vector();
+	TRAP_HANDLER_DECL;
+
+	notify_die(DIE_BREAKPOINT, "breakpoint", regs, 0, ex, SIGTRAP);
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+				    unsigned long val, void *data)
+{
+	if (val != DIE_BREAKPOINT)
+		return NOTIFY_DONE;
+
+	return hw_breakpoint_handler(data);
+}
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+	/* TODO */
+}
+
+void hw_breakpoint_pmu_unthrottle(struct perf_event *bp)
+{
+	/* TODO */
+}