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Message-Id: <200906112251.20827.rusty@rustcorp.com.au>
Date: Thu, 11 Jun 2009 22:51:20 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: paulmck@...ux.vnet.ibm.com
Cc: linux-kernel@...r.kernel.org, lguest@...abs.org
Subject: Re: [RFC PATCH v2 00/19] virtual-bus
On Sat, 6 Jun 2009 01:55:53 am Paul E. McKenney wrote:
> It is possible to get rid of the rmb() and wmb() as well, doing
> something like the following:
>
> struct lg_eventfds_num {
> unsigned int n;
> struct lg_eventfds a[0];
> }
>
> Then the rcu_dereference() gets you a pointer to a struct lg_eventfds_num,
> which has the array and its length in guaranteed synchronization without
> the need for barriers.
Yep, that's actually quite nice. The only wart is that it needs to be
allocated even when n == 0, but IMHO worth it for barrier avoidance.
This is what I ended up with:
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@...tcorp.com.au>
Cc: Davide Libenzi <davidel@...ilserver.org>
---
drivers/lguest/Kconfig | 2
drivers/lguest/core.c | 8 ++-
drivers/lguest/lg.h | 13 +++++
drivers/lguest/lguest_user.c | 98 +++++++++++++++++++++++++++++++++++++++-
include/linux/lguest_launcher.h | 1
5 files changed, 116 insertions(+), 6 deletions(-)
diff --git a/drivers/lguest/Kconfig b/drivers/lguest/Kconfig
--- 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
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -198,9 +198,11 @@ int run_guest(struct lg_cpu *cpu, unsign
/* 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
--- 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 lg
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
--- 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
}
}
+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,
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,
/* 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,
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,
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, st
* 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
--- 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.
--
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