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Date: Wed, 27 Jun 2012 15:19:46 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: avi@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
jan.kiszka@...mens.com
Subject: Re: [PATCH v2 4/6] kvm: Extend irqfd to support level interrupts
On Wed, 2012-06-27 at 12:34 +0300, Michael S. Tsirkin wrote:
> On Tue, Jun 26, 2012 at 11:09:46PM -0600, Alex Williamson wrote:
> > In order to inject an interrupt from an external source using an
> > irqfd, we need to allocate a new irq_source_id. This allows us to
> > assert and (later) de-assert an interrupt line independently from
> > users of KVM_IRQ_LINE and avoid lost interrupts.
> >
> > We also add what may appear like a bit of excessive infrastructure
> > around an object for storing this irq_source_id. However, notice
> > that we only provide a way to assert the interrupt here. A follow-on
> > interface will make use of the same irq_source_id to allow de-assert.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > ---
> >
> > Documentation/virtual/kvm/api.txt | 5 ++
> > arch/x86/kvm/x86.c | 1
> > include/linux/kvm.h | 3 +
> > virt/kvm/eventfd.c | 95 +++++++++++++++++++++++++++++++++++--
> > 4 files changed, 99 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index ea9edce..b216709 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1981,6 +1981,11 @@ the guest using the specified gsi pin. The irqfd is removed using
> > the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
> > and kvm_irqfd.gsi.
> >
> > +With KVM_IRQFD_FLAG_LEVEL KVM_IRQFD allocates a new IRQ source ID for
> > +the requested irqfd.
>
> This is the first and last time the term source id appears in this text.
> We probably can do without talking about it at all, simply
> explain that multiple irqfds mapped to same GSI are
> OR-ed together.
Ok
> > This is necessary to share level triggered
> > +interrupts with those injected through KVM_IRQ_LINE. IRQFDs created
> > +with KVM_IRQFD_FLAG_LEVEL must also set this flag when de-assiging.
> > +KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.
> >
> > 5. The kvm_run structure
> > ------------------------
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index a01a424..80bed07 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2148,6 +2148,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> > case KVM_CAP_GET_TSC_KHZ:
> > case KVM_CAP_PCI_2_3:
> > case KVM_CAP_KVMCLOCK_CTRL:
> > + case KVM_CAP_IRQFD_LEVEL:
> > r = 1;
> > break;
> > case KVM_CAP_COALESCED_MMIO:
> > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > index 2ce09aa..b2e6e4f 100644
> > --- a/include/linux/kvm.h
> > +++ b/include/linux/kvm.h
> > @@ -618,6 +618,7 @@ struct kvm_ppc_smmu_info {
> > #define KVM_CAP_PPC_GET_SMMU_INFO 78
> > #define KVM_CAP_S390_COW 79
> > #define KVM_CAP_PPC_ALLOC_HTAB 80
> > +#define KVM_CAP_IRQFD_LEVEL 81
> >
> > #ifdef KVM_CAP_IRQ_ROUTING
> >
> > @@ -683,6 +684,8 @@ struct kvm_xen_hvm_config {
> > #endif
> >
> > #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
> > +/* Available with KVM_CAP_IRQFD_LEVEL */
> > +#define KVM_IRQFD_FLAG_LEVEL (1 << 1)
> >
> > struct kvm_irqfd {
> > __u32 fd;
> > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> > index 7d7e2aa..18cc284 100644
> > --- a/virt/kvm/eventfd.c
> > +++ b/virt/kvm/eventfd.c
> > @@ -36,6 +36,64 @@
> > #include "iodev.h"
> >
> > /*
> > + * An irq_source_id can be created from KVM_IRQFD for level interrupt
> > + * injections and shared with other interfaces for EOI or de-assert.
> > + * Create an object with reference counting to make it easy to use.
> > + */
> > +struct _irq_source {
> > + int id;
> > + struct kvm *kvm;
> > + struct kref kref;
> > +};
> > +
> > +static void release_irq_source(struct kref *kref)
> > +{
> > + struct _irq_source *source;
> > +
> > + source = container_of(kref, struct _irq_source, kref);
> > +
> > + kvm_free_irq_source_id(source->kvm, source->id);
> > + kfree(source);
> > +}
> > +
>
> It would be nicer to prefix everything with irqfd_
> and generally use prefixes. _irqfd_source irqfd_source_release_ etc.
Hmm, these objects are setup by an irqfd, but I don't think that
warrants naming all the functions after irqfd. I'll make them
_irq_source_foo()
> > +static void put_irq_source(struct _irq_source *source)
> > +{
> > + if (source)
> > + kref_put(&source->kref, release_irq_source);
> > +}
> > +
> > +static struct _irq_source *__attribute__ ((used)) /* white lie for now */
> > +get_irq_source(struct _irq_source *source)
> > +{
> > + if (source)
> > + kref_get(&source->kref);
> > +
> > + return source;
> > +}
> > +
> > +static struct _irq_source *new_irq_source(struct kvm *kvm)
> > +{
> > + struct _irq_source *source;
> > + int id;
> > +
> > + source = kzalloc(sizeof(*source), GFP_KERNEL);
> > + if (!source)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + id = kvm_request_irq_source_id(kvm);
> > + if (id < 0) {
> > + kfree(source);
> > + return ERR_PTR(id);
> > + }
> > +
> > + kref_init(&source->kref);
> > + source->kvm = kvm;
> > + source->id = id;
> > +
> > + return source;
> > +}
> > +
>
> s/new/alloc/
Ok
> > +/*
> > * --------------------------------------------------------------------
> > * irqfd: Allows an fd to be used to inject an interrupt to the guest
> > *
> > @@ -52,6 +110,7 @@ struct _irqfd {
> > /* Used for level IRQ fast-path */
> > int gsi;
> > struct work_struct inject;
> > + struct _irq_source *source;
> > /* Used for setup/shutdown */
> > struct eventfd_ctx *eventfd;
> > struct list_head list;
> > @@ -62,7 +121,7 @@ struct _irqfd {
> > static struct workqueue_struct *irqfd_cleanup_wq;
> >
> > static void
> > -irqfd_inject(struct work_struct *work)
> > +irqfd_inject_edge(struct work_struct *work)
> > {
> > struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
> > struct kvm *kvm = irqfd->kvm;
> > @@ -71,6 +130,14 @@ irqfd_inject(struct work_struct *work)
> > kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
> > }
> >
> > +static void
> > +irqfd_inject_level(struct work_struct *work)
> > +{
> > + struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
> > +
> > + kvm_set_irq(irqfd->kvm, irqfd->source->id, irqfd->gsi, 1);
> > +}
> > +
> > /*
> > * Race-free decouple logic (ordering is critical)
> > */
> > @@ -96,6 +163,9 @@ irqfd_shutdown(struct work_struct *work)
> > * It is now safe to release the object's resources
> > */
> > eventfd_ctx_put(irqfd->eventfd);
> > +
> > + put_irq_source(irqfd->source);
> > +
> > kfree(irqfd);
> > }
> >
> > @@ -214,7 +284,19 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
> > irqfd->kvm = kvm;
> > irqfd->gsi = args->gsi;
> > INIT_LIST_HEAD(&irqfd->list);
> > - INIT_WORK(&irqfd->inject, irqfd_inject);
> > +
> > + if (args->flags & KVM_IRQFD_FLAG_LEVEL) {
> > + irqfd->source = new_irq_source(kvm);
> > + if (IS_ERR(irqfd->source)) {
> > + ret = PTR_ERR(irqfd->source);
> > + irqfd->source = NULL;
> > + goto fail;
>
> A bit cleaner to create a dedicated label which skips
> put_irq_source than doing source=NULL tricks.
Matter of opinion. I think I'll switch to the mechanism used elsewhere
in this function:
source = _irq_source_alloc(kvm);
if (IS_ERR(source)) {
...
}
irqfd->source = source;
> > + }
> > +
> > + INIT_WORK(&irqfd->inject, irqfd_inject_level);
> > + } else
> > + INIT_WORK(&irqfd->inject, irqfd_inject_edge);
> > +
> > INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
> >
> > file = eventfd_fget(args->fd);
> > @@ -279,9 +361,10 @@ fail:
> > if (eventfd && !IS_ERR(eventfd))
> > eventfd_ctx_put(eventfd);
> >
> > - if (!IS_ERR(file))
> > + if (file && !IS_ERR(file))
> > fput(file);
> >
> > + put_irq_source(irqfd->source);
> > kfree(irqfd);
> > return ret;
> > }
> > @@ -302,6 +385,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
> > {
> > struct _irqfd *irqfd, *tmp;
> > struct eventfd_ctx *eventfd;
> > + bool is_level = (args->flags & KVM_IRQFD_FLAG_LEVEL) != 0;
>
> != 0 is not needed here I think.
Strictly, no it's not. I just prefer to set bools from bools and I
think Avi has commented on using !! before.
> Also I'm not really sure why are we making userspace
> supply KVM_IRQFD_FLAG_LEVEL flag for clear.
It's mostly a sanity test for userspace. We don't allow duplicate
eventfds, so we really only need args->fd to match. But the existing
code matches args->gsi as well, so I thought I should make an attempt to
follow tradition. It'd be a lot easier to drop the tests below and only
match eventfd. Which do we want?
> >
> > eventfd = eventfd_ctx_fdget(args->fd);
> > if (IS_ERR(eventfd))
> > @@ -310,7 +394,8 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
> > spin_lock_irq(&kvm->irqfds.lock);
> >
> > list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
> > - if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi) {
> > + if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi &&
> > + is_level == (irqfd->source != NULL)) {
>
> Let's rename source to level_source to make usage clear?
has_source is perhaps more versatile. Thanks,
Alex
> > /*
> > * This rcu_assign_pointer is needed for when
> > * another thread calls kvm_irq_routing_update before
> > @@ -340,7 +425,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
> > int
> > kvm_irqfd(struct kvm *kvm, struct kvm_irqfd *args)
> > {
> > - if (args->flags & ~KVM_IRQFD_FLAG_DEASSIGN)
> > + if (args->flags & ~(KVM_IRQFD_FLAG_DEASSIGN | KVM_IRQFD_FLAG_LEVEL))
> > return -EINVAL;
> >
> > if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)
--
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