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Date: Fri, 5 Jun 2009 14:25:01 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Gregory Haskins <gregory.haskins@...il.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Avi Kivity <avi@...hat.com>,
Gregory Haskins <ghaskins@...ell.com>,
linux-kernel@...r.kernel.org, agraf@...e.de, pmullaney@...ell.com,
pmorreale@...ell.com, anthony@...emonkey.ws,
netdev@...r.kernel.org, kvm@...r.kernel.org,
bhutchings@...arflare.com, andi@...stfloor.org, gregkh@...e.de,
herber@...dor.apana.org.au, chrisw@...s-sol.org,
shemminger@...tta.com
Subject: Re: [RFC PATCH v2 00/19] virtual-bus
On Fri, 5 Jun 2009 04:19:17 am Gregory Haskins wrote:
> Avi Kivity wrote:
> > Gregory Haskins wrote:
> > One idea is similar to signalfd() or eventfd()
>
> And thus the "kvm-eventfd" (irqfd/iosignalfd) interface project was born.
> ;)
The lguest patch queue already has such an interface :) And I have a
partially complete in-kernel virtio_pci patch with the same trick.
I switched from "kernel created eventfd" to "userspace passes in eventfd"
after a while though; it lets you connect multiple virtqueues to a single fd
if you want.
Combined with a minor change to allow any process with access to the lguest fd
to queue interrupts, this allowed lguest to move to a thread-per-virtqueue
model which was a significant speedup as well as nice code reduction.
Here's the relevant kernel patch for reading.
Thanks!
Rusty.
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 | 9 ++++
drivers/lguest/lguest_user.c | 73 ++++++++++++++++++++++++++++++++++++++++
include/linux/lguest_launcher.h | 1
5 files changed, 89 insertions(+), 4 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 && !X86_PAE && FUTEX
+ depends on X86_32 && EXPERIMENTAL && !X86_PAE && 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 +82,11 @@ struct lg_cpu {
struct lg_cpu_arch arch;
};
+struct lg_eventfds {
+ unsigned long addr;
+ struct file *event;
+};
+
/* The private info the thread maintains about the guest. */
struct lguest
{
@@ -102,6 +107,9 @@ struct lguest
unsigned int stack_pages;
u32 tsc_khz;
+ unsigned int num_eventfds;
+ struct lg_eventfds *eventfds;
+
/* Dead? */
const char *dead;
};
@@ -152,6 +160,7 @@ 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 +37,70 @@ static int break_guest_out(struct lg_cpu
}
}
+bool send_notify_to_eventfd(struct lg_cpu *cpu)
+{
+ unsigned int i;
+
+ /* lg->eventfds is RCU-protected */
+ preempt_disable();
+ for (i = 0; i < cpu->lg->num_eventfds; i++) {
+ if (cpu->lg->eventfds[i].addr == cpu->pending_notify) {
+ eventfd_signal(cpu->lg->eventfds[i].event, 1);
+ cpu->pending_notify = 0;
+ break;
+ }
+ }
+ preempt_enable();
+ return cpu->pending_notify == 0;
+}
+
+static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
+{
+ struct lg_eventfds *new, *old;
+
+ 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) * (lg->num_eventfds + 1), GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+
+ memcpy(new, lg->eventfds, sizeof(*new) * lg->num_eventfds);
+ old = lg->eventfds;
+ lg->eventfds = new;
+ synchronize_rcu();
+ kfree(old);
+
+ lg->eventfds[lg->num_eventfds].addr = addr;
+ lg->eventfds[lg->num_eventfds].event = eventfd_fget(fd);
+ if (IS_ERR(lg->eventfds[lg->num_eventfds].event))
+ return PTR_ERR(lg->eventfds[lg->num_eventfds].event);
+
+ wmb();
+ lg->num_eventfds++;
+ 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)
@@ -260,6 +326,8 @@ 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 +365,11 @@ 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->num_eventfds; i++)
+ fput(lg->eventfds[i].event);
+
/* 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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