Date:	Mon, 18 May 2009 11:12:11 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	davide@...ilserver.org, mtosatti@...hat.com
Subject: Re: [KVM PATCH v9] kvm: add support for irqfd

Gregory Haskins wrote:
> (This is v9, applies to kvm.git:2ffc3882)
>
> KVM provides a complete virtual system environment for guests, including
> support for injecting interrupts modeled after the real exception/interrupt
> facilities present on the native platform (such as the IDT on x86).
> Virtual interrupts can come from a variety of sources (emulated devices,
> pass-through devices, etc) but all must be injected to the guest via
> the KVM infrastructure.  This patch adds a new mechanism to inject a specific
> interrupt to a guest using a decoupled eventfd mechnanism:  Any legal signal
> on the irqfd (using eventfd semantics from either userspace or kernel) will
> translate into an injected interrupt in the guest at the next available
> interrupt window.
>
> [ Changelog:
>
>    v9:
>         *) Fixed a bug in deassign where we could deadlock with the way
>            flush_work was being used (Thanks to Marcelo Tosatti's for spotting
>            this bug).
>         *) Rebased to kvm.git:2ffc3882
>
>    v8:
> 	*) Re-seperated irqfd and iofd (now called iosignalfd) into two 
>   	   distinct series.
>         *) We compare both the fd/file and gsi on deassign
>         *) De-assign is exhaustive (to support multiple associations in the
>            future)
>         *) s/KVM_CAP_EVENTFD/KVM_CAP_IRQFD
>
>    v7:
>         *) Added "iofd" to allow PIO/MMIO writes to generate an eventfd
>            signal.  This was previously discussed as "hypercallfd", but
>            since explicit hypercalls are not looking to be very popular,
>            and based on the fact that they were not going to carry payload
>            anyway, I named them "iofd".
>         *) Generalized some of the code so that irqfd and iofd could be
>            logically grouped together.  For instance
>            s/KVM_CAP_IRQFD/KVM_CAP_EVENTFD and virt/kvm/irqfd.c becomes
> 	   virt/kvm/eventfd.c
>         *) Added support for "deassign" operations to ensure we can properly
>            support hot-unplug.
> 	*) Reinstated the eventfd EXPORT_SYMBOL patch since we need it again
>            for supporting iofd.
>         *) Rebased to kvm.git:b5e725fa
>
>    v6:
>         *) Moved eventfd creation back to userspace, per Avi's request
>         *) Dropped no longer necessary supporting patches from series
>         *) Rebased to kvm.git:833367b57
>
>    v5:
>         *) Added padding to the ioctl structure
>         *) Added proper ref-count increment to the file before returning
>            success. (Needs review by Al Viro, Davide Libenzi)
> 	*) Cleaned up error-handling path to make sure we remove ourself
> 	   from the waitq if necessary.
>         *) Make sure we only add ourselves to kvm->irqfds if successful
>            creating the irqfd in the first place.
> 	*) Rebased to kvm.git:66b0aed4
>
>    v4:
>         *) Changed allocation model to create the new fd last, after
>            we get past the last potential error point by using Davide's
>            new eventfd_file_create interface (Al Viro, Davide Libenzi)
> 	*) We no longer export sys_eventfd2() since it is replaced
>            functionally with eventfd_file_create();
>         *) Rebased to kvm.git:7da2e3ba
>
>    v3:
>         *) The kernel now allocates the eventfd (need to export sys_eventfd2)
>         *) Added a flags field for future expansion to kvm_irqfd()
>         *) We properly toggle the irq level 1+0.
>         *) We re-use the USERSPACE_SRC_ID instead of creating our own
> 	*) Properly check for failures establishing a poll-table with eventfd
> 	*) Fixed fd/file leaks on failure
> 	*) Rebased to lateste kvm.git::41b76d8d04
>
>    v2:
> 	*) Dropped notifier_chain based callbacks in favor of
> 	   wait_queue_t::func and file::poll based callbacks (Thanks to
> 	   Davide for the suggestion)
>
>    v1:
>         *) Initial release
>
> ]
>
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
>
>  arch/x86/kvm/Makefile    |    2 
>  arch/x86/kvm/x86.c       |    1 
>  include/linux/kvm.h      |   11 ++
>  include/linux/kvm_host.h |    4 +
>  virt/kvm/eventfd.c       |  224 ++++++++++++++++++++++++++++++++++++++++++++++
>  virt/kvm/kvm_main.c      |   11 ++
>  6 files changed, 252 insertions(+), 1 deletions(-)
>  create mode 100644 virt/kvm/eventfd.c
>
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index b43c4ef..4d50904 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -3,7 +3,7 @@
>  #
>  
>  common-objs = $(addprefix ../../../virt/kvm/, kvm_main.o ioapic.o \
> -                coalesced_mmio.o irq_comm.o)
> +                coalesced_mmio.o irq_comm.o eventfd.o)
>  ifeq ($(CONFIG_KVM_TRACE),y)
>  common-objs += $(addprefix ../../../virt/kvm/, kvm_trace.o)
>  endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 44e87a5..123e833 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1026,6 +1026,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_REINJECT_CONTROL:
>  	case KVM_CAP_IRQ_INJECT_STATUS:
>  	case KVM_CAP_ASSIGN_DEV_IRQ:
> +	case KVM_CAP_IRQFD:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 3db5d8d..a1ecc6a 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -415,6 +415,7 @@ struct kvm_trace_rec {
>  #define KVM_CAP_ASSIGN_DEV_IRQ 29
>  /* Another bug in KVM_SET_USER_MEMORY_REGION fixed: */
>  #define KVM_CAP_JOIN_MEMORY_REGIONS_WORKS 30
> +#define KVM_CAP_IRQFD 31
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -454,6 +455,15 @@ struct kvm_irq_routing {
>  
>  #endif
>  
> +#define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
> +
> +struct kvm_irqfd {
> +	__u32 fd;
> +	__u32 gsi;
> +	__u32 flags;
> +	__u8  pad[20];
> +};
> +
>  /*
>   * ioctls for VM fds
>   */
> @@ -498,6 +508,7 @@ struct kvm_irq_routing {
>  #define KVM_ASSIGN_SET_MSIX_ENTRY \
>  			_IOW(KVMIO, 0x74, struct kvm_assigned_msix_entry)
>  #define KVM_DEASSIGN_DEV_IRQ       _IOW(KVMIO, 0x75, struct kvm_assigned_irq)
> +#define KVM_IRQFD                  _IOW(KVMIO, 0x76, struct kvm_irqfd)
>  
>  /*
>   * ioctls for vcpu fds
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8f410d3..3b6caf5 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -134,6 +134,7 @@ struct kvm {
>  	struct list_head vm_list;
>  	struct kvm_io_bus mmio_bus;
>  	struct kvm_io_bus pio_bus;
> +	struct list_head irqfds;
>  	struct kvm_vm_stat stat;
>  	struct kvm_arch arch;
>  	atomic_t users_count;
> @@ -528,4 +529,7 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {}
>  
>  #endif
>  
> +int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags);
> +void kvm_irqfd_release(struct kvm *kvm);
> +
>  #endif
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> new file mode 100644
> index 0000000..41897f9
> --- /dev/null
> +++ b/virt/kvm/eventfd.c
> @@ -0,0 +1,224 @@
> +/*
> + * kvm eventfd support - use eventfd objects to signal various KVM events
> + *
> + * Copyright 2009 Novell.  All Rights Reserved.
> + *
> + * Author:
> + *	Gregory Haskins <ghaskins@...ell.com>
> + *
> + * This file is free software; you can redistribute it and/or modify
> + * it under the terms of version 2 of the GNU General Public License
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software Foundation,
> + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
> + */
> +
> +#include <linux/kvm_host.h>
> +#include <linux/workqueue.h>
> +#include <linux/syscalls.h>
> +#include <linux/wait.h>
> +#include <linux/poll.h>
> +#include <linux/file.h>
> +#include <linux/list.h>
> +
> +/*
> + * --------------------------------------------------------------------
> + * irqfd: Allows an fd to be used to inject an interrupt to the guest
> + *
> + * Credit goes to Avi Kivity for the original idea.
> + * --------------------------------------------------------------------
> + */
> +struct _irqfd {
> +	struct kvm               *kvm;
> +	int                       gsi;
> +	struct file              *file;
> +	struct list_head          list;
> +	poll_table                pt;
> +	wait_queue_head_t        *wqh;
> +	wait_queue_t              wait;
> +	struct work_struct        work;
> +};
> +
> +static void
> +irqfd_inject(struct work_struct *work)
> +{
> +	struct _irqfd *irqfd = container_of(work, struct _irqfd, work);
> +	struct kvm *kvm = irqfd->kvm;
> +
> +	mutex_lock(&kvm->lock);
> +	kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
> +	kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
> +	mutex_unlock(&kvm->lock);
> +}
> +
> +static int
> +irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
> +{
> +	struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
> +
> +	/*
> +	 * The wake_up with interrupts disabled.  Therefore we need to defer
> +	 * the IRQ injection until later since we need to acquire the
> +	 * kvm->lock to do so.
> +	 */
> +	schedule_work(&irqfd->work);
> +
> +	return 0;
> +}
> +
> +static void
> +irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
> +			poll_table *pt)
> +{
> +	struct _irqfd *irqfd = container_of(pt, struct _irqfd, pt);
> +
> +	irqfd->wqh = wqh;
> +	add_wait_queue(wqh, &irqfd->wait);
> +}
> +
> +static int
> +kvm_assign_irqfd(struct kvm *kvm, int fd, int gsi)
> +{
> +	struct _irqfd *irqfd;
> +	struct file *file = NULL;
> +	int ret;
> +
> +	irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
> +	if (!irqfd)
> +		return -ENOMEM;
> +
> +	irqfd->kvm = kvm;
> +	irqfd->gsi = gsi;
> +	INIT_LIST_HEAD(&irqfd->list);
> +	INIT_WORK(&irqfd->work, irqfd_inject);
> +
> +	/*
> +	 * Embed the file* lifetime in the irqfd.
> +	 */
> +	file = fget(fd);
> +	if (IS_ERR(file)) {
> +		ret = PTR_ERR(file);
> +		goto fail;
> +	}
> +
> +	/*
> +	 * Install our own custom wake-up handling so we are notified via
> +	 * a callback whenever someone signals the underlying eventfd
> +	 */
> +	init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
> +	init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
> +
> +	ret = file->f_op->poll(file, &irqfd->pt);
> +	if (ret < 0)
> +		goto fail;
> +
> +	irqfd->file = file;
> +
> +	mutex_lock(&kvm->lock);
> +	list_add_tail(&irqfd->list, &kvm->irqfds);
> +	mutex_unlock(&kvm->lock);
> +
> +	return 0;
> +
> +fail:
> +	if (irqfd->wqh)
> +		remove_wait_queue(irqfd->wqh, &irqfd->wait);
> +
> +	if (file && !IS_ERR(file))
> +		fput(file);
> +
> +	kfree(irqfd);
> +	return ret;
> +}
> +
> +static void
> +irqfd_release(struct _irqfd *irqfd)
> +{
> +	/*
> +	 * The ordering is important.  We must remove ourselves from the wqh
> +	 * first to ensure no more event callbacks are issued, and then flush
> +	 * any previously scheduled work prior to freeing the memory
> +	 */
> +	remove_wait_queue(irqfd->wqh, &irqfd->wait);
> +
> +	flush_work(&irqfd->work);
> +
> +	fput(irqfd->file);
> +	kfree(irqfd);
> +}
> +
> +static struct _irqfd *irqfd_remove(struct kvm *kvm, struct file *file, int gsi)
> +{
> +	struct _irqfd *irqfd;
> +
> +	mutex_lock(&kvm->lock);
> +
> +	/*
> +	 * linear search isn't brilliant, but this should be a infrequent
> +	 * operation and the list should not grow very large
> +	 */
> +	list_for_each_entry(irqfd, &kvm->irqfds, list) {
> +		if (irqfd->file != file || irqfd->gsi != gsi)
> +			continue;
> +
> +		list_del(&irqfd->list);
> +		mutex_unlock(&kvm->lock);
> +
> +		return irqfd;
> +	}
> +
> +	mutex_unlock(&kvm->lock);
> +
> +	return NULL;
> +}
> +
> +static int
> +kvm_deassign_irqfd(struct kvm *kvm, int fd, int gsi)
> +{
> +	struct _irqfd *irqfd;
> +	struct file *file;
> +
> +	file = fget(fd);
> +	if (IS_ERR(file))
> +		return PTR_ERR(file);
> +
> +	while ((irqfd = irqfd_remove(kvm, file, gsi)))
> +		/*
> +		 * We remove the item from the list under the lock, but we
> +		 * free it outside the lock to avoid deadlocking with the
> +		 * flush_work and the work_item taking the lock
> +		 */
> +		irqfd_release(irqfd);
> +
> +	fput(file);
> +
> +	return -ENOENT;
>   

More slop.  I shouldn't send patches out first thing Monday morning, I
guess.

Here is my current delta queued for v10.  I will wait for some feedback
on v9 before cutting it:

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 41897f9..5e07e8b 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -154,7 +154,8 @@ irqfd_release(struct _irqfd *irqfd)
        kfree(irqfd);
 }
 
-static struct _irqfd *irqfd_remove(struct kvm *kvm, struct file *file,
int gsi)
+static struct _irqfd *
+irqfd_remove(struct kvm *kvm, struct file *file, int gsi)
 {
        struct _irqfd *irqfd;
 
@@ -184,22 +185,25 @@ kvm_deassign_irqfd(struct kvm *kvm, int fd, int gsi)
 {
        struct _irqfd *irqfd;
        struct file *file;
+       int count = 0;
 
        file = fget(fd);
        if (IS_ERR(file))
                return PTR_ERR(file);
 
-       while ((irqfd = irqfd_remove(kvm, file, gsi)))
+       while ((irqfd = irqfd_remove(kvm, file, gsi))) {
                /*
                 * We remove the item from the list under the lock, but we
                 * free it outside the lock to avoid deadlocking with the
                 * flush_work and the work_item taking the lock
                 */
                irqfd_release(irqfd);
+               count++;
+       }
 
        fput(file);
 
-       return -ENOENT;
+       return count ? count : -ENOENT;
 }

> +}
> +
> +int
> +kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
> +{
> +	if (flags & KVM_IRQFD_FLAG_DEASSIGN)
> +		return kvm_deassign_irqfd(kvm, fd, gsi);
> +
> +	return kvm_assign_irqfd(kvm, fd, gsi);
> +}
> +
> +void
> +kvm_irqfd_release(struct kvm *kvm)
> +{
> +	struct _irqfd *irqfd, *tmp;
> +
> +	/* don't bother with the lock..we are shutting down */
> +	list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds, list) {
> +		list_del(&irqfd->list);
> +		irqfd_release(irqfd);
> +	}
> +}
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index bebfe59..b58837d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -983,6 +983,7 @@ static struct kvm *kvm_create_vm(void)
>  	atomic_inc(&kvm->mm->mm_count);
>  	spin_lock_init(&kvm->mmu_lock);
>  	kvm_io_bus_init(&kvm->pio_bus);
> +	INIT_LIST_HEAD(&kvm->irqfds);
>  	mutex_init(&kvm->lock);
>  	kvm_io_bus_init(&kvm->mmio_bus);
>  	init_rwsem(&kvm->slots_lock);
> @@ -1034,6 +1035,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
>  	spin_lock(&kvm_lock);
>  	list_del(&kvm->vm_list);
>  	spin_unlock(&kvm_lock);
> +	kvm_irqfd_release(kvm);
>  	kvm_free_irq_routing(kvm);
>  	kvm_io_bus_destroy(&kvm->pio_bus);
>  	kvm_io_bus_destroy(&kvm->mmio_bus);
> @@ -2210,6 +2212,15 @@ static long kvm_vm_ioctl(struct file *filp,
>  	}
>  #endif
>  #endif /* KVM_CAP_IRQ_ROUTING */
> +	case KVM_IRQFD: {
> +		struct kvm_irqfd data;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&data, argp, sizeof data))
> +			goto out;
> +		r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags);
> +		break;
> +	}
>  	default:
>  		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
>  	}
>
> --
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>   



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