Commit df60aeef authored by Rusty Russell's avatar Rusty Russell
Browse files

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: default avatarRusty Russell <rusty@rustcorp.com.au>
Cc: Davide Libenzi <davidel@xmailserver.org>
parent 5718607b
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
......
......@@ -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 */
......
......@@ -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);
......
......@@ -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))
......
......@@ -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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