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Subject[patch 06/28]xen: xen event channels
Xen implements interrupts in terms of event channels.  This patch maps
an event through an event channel to an irq, and then feeds it through
the normal interrupt path, via a Xen irq_chip implementation.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Eric W. Biederman <ebiederm@xmission.com>

---
arch/i386/xen/Makefile | 3
arch/i386/xen/enlighten.c | 1
arch/i386/xen/events.c | 511 +++++++++++++++++++++++++++++++++++++++++++++
include/xen/events.h | 28 ++
4 files changed, 542 insertions(+), 1 deletion(-)
===================================================================
--- a/arch/i386/xen/Makefile
+++ b/arch/i386/xen/Makefile
@@ -1,1 +1,2 @@ obj-y := enlighten.o setup.o features.o
-obj-y := enlighten.o setup.o features.o multicalls.o mmu.o
+obj-y := enlighten.o setup.o features.o multicalls.o mmu.o \
+ events.o
===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -593,6 +593,7 @@ static const struct paravirt_ops xen_par

.memory_setup = xen_memory_setup,
.arch_setup = xen_arch_setup,
+ .init_IRQ = xen_init_IRQ,

.cpuid = xen_cpuid,

===================================================================
--- /dev/null
+++ b/arch/i386/xen/events.c
@@ -0,0 +1,511 @@
+/*
+ * Xen event channels
+ *
+ * Xen models interrupts with abstract event channels. Because each
+ * domain gets 1024 event channels, but NR_IRQ is not that large, we
+ * must dynamically map irqs<->event channels. The event channels
+ * interface with the rest of the kernel by defining a xen interrupt
+ * chip. When an event is recieved, it is mapped to an irq and sent
+ * through the normal interrupt processing path.
+ *
+ * There are four kinds of events which can be mapped to an event
+ * channel:
+ *
+ * 1. Inter-domain notifications. This includes all the virtual
+ * device events, since they're driven by front-ends in another domain
+ * (typically dom0).
+ * 2. VIRQs, typically used for timers. These are per-cpu events.
+ * 3. IPIs.
+ * 4. Hardware interrupts. Not supported at present.
+ *
+ * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
+ */
+
+#include <linux/linkage.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+#include <asm/ptrace.h>
+#include <asm/irq.h>
+#include <asm/sync_bitops.h>
+#include <asm/xen/hypercall.h>
+
+#include <xen/events.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/event_channel.h>
+
+#include "xen-ops.h"
+
+/*
+ * This lock protects updates to the following mapping and reference-count
+ * arrays. The lock does not need to be acquired to read the mapping tables.
+ */
+static DEFINE_SPINLOCK(irq_mapping_update_lock);
+
+/* IRQ <-> VIRQ mapping. */
+static DEFINE_PER_CPU(int, virq_to_irq[NR_VIRQS]) = {[0 ... NR_VIRQS-1] = -1};
+
+/* Packed IRQ information: binding type, sub-type index, and event channel. */
+struct packed_irq
+{
+ unsigned short evtchn;
+ unsigned char index;
+ unsigned char type;
+};
+
+static struct packed_irq irq_info[NR_IRQS];
+
+/* Binding types. */
+enum { IRQT_UNBOUND, IRQT_PIRQ, IRQT_VIRQ, IRQT_IPI, IRQT_EVTCHN };
+
+/* Convenient shorthand for packed representation of an unbound IRQ. */
+#define IRQ_UNBOUND mk_irq_info(IRQT_UNBOUND, 0, 0)
+
+static int evtchn_to_irq[NR_EVENT_CHANNELS] = {
+ [0 ... NR_EVENT_CHANNELS-1] = -1
+};
+static unsigned long cpu_evtchn_mask[NR_CPUS][NR_EVENT_CHANNELS/BITS_PER_LONG];
+static u8 cpu_evtchn[NR_EVENT_CHANNELS];
+
+/* Reference counts for bindings to IRQs. */
+static int irq_bindcount[NR_IRQS];
+
+/* Xen will never allocate port zero for any purpose. */
+#define VALID_EVTCHN(chn) ((chn) != 0)
+
+/*
+ * Force a proper event-channel callback from Xen after clearing the
+ * callback mask. We do this in a very simple manner, by making a call
+ * down into Xen. The pending flag will be checked by Xen on return.
+ */
+void force_evtchn_callback(void)
+{
+ (void)HYPERVISOR_xen_version(0, NULL);
+}
+EXPORT_SYMBOL_GPL(force_evtchn_callback);
+
+static struct irq_chip xen_dynamic_chip;
+
+/* Constructor for packed IRQ information. */
+static inline struct packed_irq mk_irq_info(u32 type, u32 index, u32 evtchn)
+{
+ return (struct packed_irq) { evtchn, index, type };
+}
+
+/*
+ * Accessors for packed IRQ information.
+ */
+static inline unsigned int evtchn_from_irq(int irq)
+{
+ return irq_info[irq].evtchn;
+}
+
+static inline unsigned int index_from_irq(int irq)
+{
+ return irq_info[irq].index;
+}
+
+static inline unsigned int type_from_irq(int irq)
+{
+ return irq_info[irq].type;
+}
+
+static inline unsigned long active_evtchns(unsigned int cpu,
+ struct shared_info *sh,
+ unsigned int idx)
+{
+ return (sh->evtchn_pending[idx] &
+ cpu_evtchn_mask[cpu][idx] &
+ ~sh->evtchn_mask[idx]);
+}
+
+static void bind_evtchn_to_cpu(unsigned int chn, unsigned int cpu)
+{
+ int irq = evtchn_to_irq[chn];
+
+ BUG_ON(irq == -1);
+#ifdef CONFIG_SMP
+ irq_desc[irq].affinity = cpumask_of_cpu(cpu);
+#endif
+
+ __clear_bit(chn, cpu_evtchn_mask[cpu_evtchn[chn]]);
+ __set_bit(chn, cpu_evtchn_mask[cpu]);
+
+ cpu_evtchn[chn] = cpu;
+}
+
+static void init_evtchn_cpu_bindings(void)
+{
+#ifdef CONFIG_SMP
+ int i;
+ /* By default all event channels notify CPU#0. */
+ for (i = 0; i < NR_IRQS; i++)
+ irq_desc[i].affinity = cpumask_of_cpu(0);
+#endif
+
+ memset(cpu_evtchn, 0, sizeof(cpu_evtchn));
+ memset(cpu_evtchn_mask[0], ~0, sizeof(cpu_evtchn_mask[0]));
+}
+
+static inline unsigned int cpu_from_evtchn(unsigned int evtchn)
+{
+ return cpu_evtchn[evtchn];
+}
+
+static inline void clear_evtchn(int port)
+{
+ struct shared_info *s = HYPERVISOR_shared_info;
+ sync_clear_bit(port, &s->evtchn_pending[0]);
+}
+
+static inline void set_evtchn(int port)
+{
+ struct shared_info *s = HYPERVISOR_shared_info;
+ sync_set_bit(port, &s->evtchn_pending[0]);
+}
+
+
+/**
+ * notify_remote_via_irq - send event to remote end of event channel via irq
+ * @irq: irq of event channel to send event to
+ *
+ * Unlike notify_remote_via_evtchn(), this is safe to use across
+ * save/restore. Notifications on a broken connection are silently
+ * dropped.
+ */
+void notify_remote_via_irq(int irq)
+{
+ int evtchn = evtchn_from_irq(irq);
+
+ if (VALID_EVTCHN(evtchn))
+ notify_remote_via_evtchn(evtchn);
+}
+EXPORT_SYMBOL_GPL(notify_remote_via_irq);
+
+static void mask_evtchn(int port)
+{
+ struct shared_info *s = HYPERVISOR_shared_info;
+ sync_set_bit(port, &s->evtchn_mask[0]);
+}
+
+static void unmask_evtchn(int port)
+{
+ struct shared_info *s = HYPERVISOR_shared_info;
+ unsigned int cpu = get_cpu();
+
+ BUG_ON(!irqs_disabled());
+
+ /* Slow path (hypercall) if this is a non-local port. */
+ if (unlikely(cpu != cpu_from_evtchn(port))) {
+ struct evtchn_unmask unmask = { .port = port };
+ (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
+ } else {
+ struct vcpu_info *vcpu_info = __get_cpu_var(xen_vcpu);
+
+ sync_clear_bit(port, &s->evtchn_mask[0]);
+
+ /*
+ * The following is basically the equivalent of
+ * 'hw_resend_irq'. Just like a real IO-APIC we 'lose
+ * the interrupt edge' if the channel is masked.
+ */
+ if (sync_test_bit(port, &s->evtchn_pending[0]) &&
+ !sync_test_and_set_bit(port / BITS_PER_LONG,
+ &vcpu_info->evtchn_pending_sel))
+ vcpu_info->evtchn_upcall_pending = 1;
+ }
+
+ put_cpu();
+}
+
+static int find_unbound_irq(void)
+{
+ int irq;
+
+ /* Only allocate from dynirq range */
+ for (irq = 0; irq < NR_IRQS; irq++)
+ if (irq_bindcount[irq] == 0)
+ break;
+
+ if (irq == NR_IRQS)
+ panic("No available IRQ to bind to: increase NR_IRQS!\n");
+
+ return irq;
+}
+
+static int bind_evtchn_to_irq(unsigned int evtchn)
+{
+ int irq;
+
+ spin_lock(&irq_mapping_update_lock);
+
+ irq = evtchn_to_irq[evtchn];
+
+ if (irq == -1) {
+ irq = find_unbound_irq();
+
+ dynamic_irq_init(irq);
+ set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
+ handle_level_irq, "event");
+
+ evtchn_to_irq[evtchn] = irq;
+ irq_info[irq] = mk_irq_info(IRQT_EVTCHN, 0, evtchn);
+ }
+
+ irq_bindcount[irq]++;
+
+ spin_unlock(&irq_mapping_update_lock);
+
+ return irq;
+}
+
+static int bind_virq_to_irq(unsigned int virq, unsigned int cpu)
+{
+ struct evtchn_bind_virq bind_virq;
+ int evtchn, irq;
+
+ spin_lock(&irq_mapping_update_lock);
+
+ irq = per_cpu(virq_to_irq, cpu)[virq];
+
+ if (irq == -1) {
+ bind_virq.virq = virq;
+ bind_virq.vcpu = cpu;
+ if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
+ &bind_virq) != 0)
+ BUG();
+ evtchn = bind_virq.port;
+
+ irq = find_unbound_irq();
+
+ dynamic_irq_init(irq);
+ set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
+ handle_level_irq, "virq");
+
+ evtchn_to_irq[evtchn] = irq;
+ irq_info[irq] = mk_irq_info(IRQT_VIRQ, virq, evtchn);
+
+ per_cpu(virq_to_irq, cpu)[virq] = irq;
+
+ bind_evtchn_to_cpu(evtchn, cpu);
+ }
+
+ irq_bindcount[irq]++;
+
+ spin_unlock(&irq_mapping_update_lock);
+
+ return irq;
+}
+
+static void unbind_from_irq(unsigned int irq)
+{
+ struct evtchn_close close;
+ int evtchn = evtchn_from_irq(irq);
+
+ spin_lock(&irq_mapping_update_lock);
+
+ if (VALID_EVTCHN(evtchn) && (--irq_bindcount[irq] == 0)) {
+ close.port = evtchn;
+ if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
+ BUG();
+
+ switch (type_from_irq(irq)) {
+ case IRQT_VIRQ:
+ per_cpu(virq_to_irq, cpu_from_evtchn(evtchn))
+ [index_from_irq(irq)] = -1;
+ break;
+ default:
+ break;
+ }
+
+ /* Closed ports are implicitly re-bound to VCPU0. */
+ bind_evtchn_to_cpu(evtchn, 0);
+
+ evtchn_to_irq[evtchn] = -1;
+ irq_info[irq] = IRQ_UNBOUND;
+
+ dynamic_irq_init(irq);
+ }
+
+ spin_unlock(&irq_mapping_update_lock);
+}
+
+int bind_evtchn_to_irqhandler(unsigned int evtchn,
+ irqreturn_t (*handler)(int, void *),
+ unsigned long irqflags,
+ const char *devname, void *dev_id)
+{
+ unsigned int irq;
+ int retval;
+
+ irq = bind_evtchn_to_irq(evtchn);
+ retval = request_irq(irq, handler, irqflags, devname, dev_id);
+ if (retval != 0) {
+ unbind_from_irq(irq);
+ return retval;
+ }
+
+ return irq;
+}
+EXPORT_SYMBOL_GPL(bind_evtchn_to_irqhandler);
+
+int bind_virq_to_irqhandler(unsigned int virq, unsigned int cpu,
+ irqreturn_t (*handler)(int, void *),
+ unsigned long irqflags, const char *devname, void *dev_id)
+{
+ unsigned int irq;
+ int retval;
+
+ irq = bind_virq_to_irq(virq, cpu);
+ retval = request_irq(irq, handler, irqflags, devname, dev_id);
+ if (retval != 0) {
+ unbind_from_irq(irq);
+ return retval;
+ }
+
+ return irq;
+}
+EXPORT_SYMBOL_GPL(bind_virq_to_irqhandler);
+
+void unbind_from_irqhandler(unsigned int irq, void *dev_id)
+{
+ free_irq(irq, dev_id);
+ unbind_from_irq(irq);
+}
+EXPORT_SYMBOL_GPL(unbind_from_irqhandler);
+
+/*
+ * Search the CPUs pending events bitmasks. For each one found, map
+ * the event number to an irq, and feed it into do_IRQ() for
+ * handling.
+ *
+ * Xen uses a two-level bitmap to speed searching. The first level is
+ * a bitset of words which contain pending event bits. The second
+ * level is a bitset of pending events themselves.
+ */
+fastcall void xen_evtchn_do_upcall(struct pt_regs *regs)
+{
+ int cpu = get_cpu();
+ struct shared_info *s = HYPERVISOR_shared_info;
+ struct vcpu_info *vcpu_info = __get_cpu_var(xen_vcpu);
+ unsigned long pending_words;
+
+ vcpu_info->evtchn_upcall_pending = 0;
+
+ /* NB. No need for a barrier here -- XCHG is a barrier on x86. */
+ pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
+ while (pending_words != 0) {
+ unsigned long pending_bits;
+ int word_idx = __ffs(pending_words);
+ pending_words &= ~(1UL << word_idx);
+
+ while ((pending_bits = active_evtchns(cpu, s, word_idx)) != 0) {
+ int bit_idx = __ffs(pending_bits);
+ int port = (word_idx * BITS_PER_LONG) + bit_idx;
+ int irq = evtchn_to_irq[port];
+
+ if (irq != -1) {
+ regs->orig_eax = ~irq;
+ do_IRQ(regs);
+ }
+ }
+ }
+
+ put_cpu();
+}
+
+/* Rebind an evtchn so that it gets delivered to a specific cpu */
+static void rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
+{
+ struct evtchn_bind_vcpu bind_vcpu;
+ int evtchn = evtchn_from_irq(irq);
+
+ if (!VALID_EVTCHN(evtchn))
+ return;
+
+ /* Send future instances of this interrupt to other vcpu. */
+ bind_vcpu.port = evtchn;
+ bind_vcpu.vcpu = tcpu;
+
+ /*
+ * If this fails, it usually just indicates that we're dealing with a
+ * virq or IPI channel, which don't actually need to be rebound. Ignore
+ * it, but don't do the xenlinux-level rebind in that case.
+ */
+ if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_vcpu, &bind_vcpu) >= 0)
+ bind_evtchn_to_cpu(evtchn, tcpu);
+}
+
+
+static void set_affinity_irq(unsigned irq, cpumask_t dest)
+{
+ unsigned tcpu = first_cpu(dest);
+ rebind_irq_to_cpu(irq, tcpu);
+}
+
+static void enable_dynirq(unsigned int irq)
+{
+ int evtchn = evtchn_from_irq(irq);
+
+ if (VALID_EVTCHN(evtchn))
+ unmask_evtchn(evtchn);
+}
+
+static void disable_dynirq(unsigned int irq)
+{
+ int evtchn = evtchn_from_irq(irq);
+
+ if (VALID_EVTCHN(evtchn))
+ mask_evtchn(evtchn);
+}
+
+static void ack_dynirq(unsigned int irq)
+{
+ int evtchn = evtchn_from_irq(irq);
+
+ move_native_irq(irq);
+
+ if (VALID_EVTCHN(evtchn))
+ clear_evtchn(evtchn);
+}
+
+static int retrigger_dynirq(unsigned int irq)
+{
+ int evtchn = evtchn_from_irq(irq);
+ int ret = 0;
+
+ if (VALID_EVTCHN(evtchn)) {
+ set_evtchn(evtchn);
+ ret = 1;
+ }
+
+ return ret;
+}
+
+static struct irq_chip xen_dynamic_chip __read_mostly = {
+ .name = "xen-dyn",
+ .mask = disable_dynirq,
+ .unmask = enable_dynirq,
+ .ack = ack_dynirq,
+ .set_affinity = set_affinity_irq,
+ .retrigger = retrigger_dynirq,
+};
+
+void __init xen_init_IRQ(void)
+{
+ int i;
+
+ init_evtchn_cpu_bindings();
+
+ /* No event channels are 'live' right now. */
+ for (i = 0; i < NR_EVENT_CHANNELS; i++)
+ mask_evtchn(i);
+
+ /* Dynamic IRQ space is currently unbound. Zero the refcnts. */
+ for (i = 0; i < NR_IRQS; i++)
+ irq_bindcount[i] = 0;
+
+ irq_ctx_init(smp_processor_id());
+}
===================================================================
--- /dev/null
+++ b/include/xen/events.h
@@ -0,0 +1,28 @@
+#ifndef _XEN_EVENTS_H
+#define _XEN_EVENTS_H
+
+#include <linux/irq.h>
+
+int bind_evtchn_to_irqhandler(unsigned int evtchn,
+ irqreturn_t (*handler)(int, void *),
+ unsigned long irqflags, const char *devname,
+ void *dev_id);
+int bind_virq_to_irqhandler(unsigned int virq, unsigned int cpu,
+ irqreturn_t (*handler)(int, void *),
+ unsigned long irqflags, const char *devname, void *dev_id);
+
+/*
+ * Common unbind function for all event sources. Takes IRQ to unbind from.
+ * Automatically closes the underlying event channel (even for bindings
+ * made with bind_evtchn_to_irqhandler()).
+ */
+void unbind_from_irqhandler(unsigned int irq, void *dev_id);
+
+static inline void notify_remote_via_evtchn(int port)
+{
+ struct evtchn_send send = { .port = port };
+ (void)HYPERVISOR_event_channel_op(EVTCHNOP_send, &send);
+}
+
+extern void notify_remote_via_irq(int irq);
+#endif /* _XEN_EVENTS_H */
--

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