lguest: use eventfds for device notification

Currently, when a Guest wants to perform I/O it calls LHCALL_NOTIFY with
an address: the main Launcher process returns with this address, and figures
out what device to run.

A far nicer model is to let processes bind an eventfd to an address: if we
find one, we simply signal the eventfd.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Davide Libenzi <davidel@xmailserver.org>

5 files changed, 116 insertions, 6 deletions

diff --git a/drivers/lguest/Kconfig b/drivers/lguest/Kconfig
index 8f63845db830..0aaa0597a622 100644
--- a/drivers/lguest/Kconfig
+++ b/drivers/lguest/Kconfig
@@ -1,6 +1,6 @@
 config LGUEST
         tristate "Linux hypervisor example code"
-        depends on X86_32 && EXPERIMENTAL && FUTEX
+        depends on X86_32 && EXPERIMENTAL && EVENTFD
         select HVC_DRIVER
         ---help---
           This is a very simple module which allows you to run
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index d0298dc45d97..508569c9571a 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -198,9 +198,11 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                 /* It's possible the Guest did a NOTIFY hypercall to the
                  * Launcher, in which case we return from the read() now. */
                 if (cpu->pending_notify) {
-                        if (put_user(cpu->pending_notify, user))
-                                return -EFAULT;
-                        return sizeof(cpu->pending_notify);
+                        if (!send_notify_to_eventfd(cpu)) {
+                                if (put_user(cpu->pending_notify, user))
+                                        return -EFAULT;
+                                return sizeof(cpu->pending_notify);
+                        }
                 }
 
                 /* Check for signals */
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 040cb70780e7..32fefdc6ad3e 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -82,6 +82,16 @@ struct lg_cpu {
         struct lg_cpu_arch arch;
 };
 
+struct lg_eventfd {
+        unsigned long addr;
+        struct file *event;
+};
+
+struct lg_eventfd_map {
+        unsigned int num;
+        struct lg_eventfd map[];
+};
+
 /* The private info the thread maintains about the guest. */
 struct lguest
 {
@@ -102,6 +112,8 @@ struct lguest
         unsigned int stack_pages;
         u32 tsc_khz;
 
+        struct lg_eventfd_map *eventfds;
+
         /* Dead? */
         const char *dead;
 };
@@ -154,6 +166,7 @@ void setup_default_idt_entries(struct lguest_ro_state *state,
 void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
                 const unsigned long *def);
 void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta);
+bool send_notify_to_eventfd(struct lg_cpu *cpu);
 void init_clockdev(struct lg_cpu *cpu);
 bool check_syscall_vector(struct lguest *lg);
 int init_interrupts(void);
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 1982b45bd935..f6bf255f1837 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -7,6 +7,8 @@
 #include <linux/miscdevice.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
+#include <linux/eventfd.h>
+#include <linux/file.h>
 #include "lg.h"
 
 /*L:055 When something happens, the Waker process needs a way to stop the
@@ -35,6 +37,81 @@ static int break_guest_out(struct lg_cpu *cpu, const unsigned long __user*input)
         }
 }
 
+bool send_notify_to_eventfd(struct lg_cpu *cpu)
+{
+        unsigned int i;
+        struct lg_eventfd_map *map;
+
+        /* lg->eventfds is RCU-protected */
+        rcu_read_lock();
+        map = rcu_dereference(cpu->lg->eventfds);
+        for (i = 0; i < map->num; i++) {
+                if (map->map[i].addr == cpu->pending_notify) {
+                        eventfd_signal(map->map[i].event, 1);
+                        cpu->pending_notify = 0;
+                        break;
+                }
+        }
+        rcu_read_unlock();
+        return cpu->pending_notify == 0;
+}
+
+static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
+{
+        struct lg_eventfd_map *new, *old = lg->eventfds;
+
+        if (!addr)
+                return -EINVAL;
+
+        /* Replace the old array with the new one, carefully: others can
+         * be accessing it at the same time */
+        new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
+                      GFP_KERNEL);
+        if (!new)
+                return -ENOMEM;
+
+        /* First make identical copy. */
+        memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
+        new->num = old->num;
+
+        /* Now append new entry. */
+        new->map[new->num].addr = addr;
+        new->map[new->num].event = eventfd_fget(fd);
+        if (IS_ERR(new->map[new->num].event)) {
+                kfree(new);
+                return PTR_ERR(new->map[new->num].event);
+        }
+        new->num++;
+
+        /* Now put new one in place. */
+        rcu_assign_pointer(lg->eventfds, new);
+
+        /* We're not in a big hurry.  Wait until noone's looking at old
+         * version, then delete it. */
+        synchronize_rcu();
+        kfree(old);
+
+        return 0;
+}
+
+static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
+{
+        unsigned long addr, fd;
+        int err;
+
+        if (get_user(addr, input) != 0)
+                return -EFAULT;
+        input++;
+        if (get_user(fd, input) != 0)
+                return -EFAULT;
+
+        mutex_lock(&lguest_lock);
+        err = add_eventfd(lg, addr, fd);
+        mutex_unlock(&lguest_lock);
+
+        return 0;
+}
+
 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
  * number to /dev/lguest. */
 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
@@ -184,6 +261,13 @@ static int initialize(struct file *file, const unsigned long __user *input)
                 goto unlock;
         }
 
+        lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
+        if (!lg->eventfds) {
+                err = -ENOMEM;
+                goto free_lg;
+        }
+        lg->eventfds->num = 0;
+
         /* Populate the easy fields of our "struct lguest" */
         lg->mem_base = (void __user *)args[0];
         lg->pfn_limit = args[1];
@@ -191,7 +275,7 @@ static int initialize(struct file *file, const unsigned long __user *input)
         /* This is the first cpu (cpu 0) and it will start booting at args[2] */
         err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
         if (err)
-                goto release_guest;
+                goto free_eventfds;
 
         /* Initialize the Guest's shadow page tables, using the toplevel
          * address the Launcher gave us.  This allocates memory, so can fail. */
@@ -210,7 +294,9 @@ static int initialize(struct file *file, const unsigned long __user *input)
 free_regs:
         /* FIXME: This should be in free_vcpu */
         free_page(lg->cpus[0].regs_page);
-release_guest:
+free_eventfds:
+        kfree(lg->eventfds);
+free_lg:
         kfree(lg);
 unlock:
         mutex_unlock(&lguest_lock);
@@ -260,6 +346,8 @@ static ssize_t write(struct file *file, const char __user *in,
                 return user_send_irq(cpu, input);
         case LHREQ_BREAK:
                 return break_guest_out(cpu, input);
+        case LHREQ_EVENTFD:
+                return attach_eventfd(lg, input);
         default:
                 return -EINVAL;
         }
@@ -297,6 +385,12 @@ static int close(struct inode *inode, struct file *file)
                  * the Launcher's memory management structure. */
                 mmput(lg->cpus[i].mm);
         }
+
+        /* Release any eventfds they registered. */
+        for (i = 0; i < lg->eventfds->num; i++)
+                fput(lg->eventfds->map[i].event);
+        kfree(lg->eventfds);
+
         /* If lg->dead doesn't contain an error code it will be NULL or a
          * kmalloc()ed string, either of which is ok to hand to kfree(). */
         if (!IS_ERR(lg->dead))
diff --git a/include/linux/lguest_launcher.h b/include/linux/lguest_launcher.h
index a53407a4165c..9de964b90586 100644
--- a/include/linux/lguest_launcher.h
+++ b/include/linux/lguest_launcher.h
@@ -58,6 +58,7 @@ enum lguest_req
         LHREQ_GETDMA, /* No longer used */
         LHREQ_IRQ, /* + irq */
         LHREQ_BREAK, /* + on/off flag (on blocks until someone does off) */
+        LHREQ_EVENTFD, /* + address, fd. */
 };
 
 /* The alignment to use between consumer and producer parts of vring.