Re: [PATCH v8 3/6] kvm: Add IRQ source ID option to KVM_IRQFD

Alex Williamson
2012-08-15T17:08:41Z

On Wed, 2012-08-15 at 16:49 +0300, Michael S. Tsirkin wrote:
> On Fri, Aug 10, 2012 at 04:37:33PM -0600, Alex Williamson wrote:
> > This allows specifying an IRQ source ID to be used when injecting an
> > interrupt. When not specified KVM_USERSPACE_IRQ_SOURCE_ID is used.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---
> >
> > Documentation/virtual/kvm/api.txt | 5 +++++
> > arch/x86/kvm/x86.c | 1 +
> > include/linux/kvm.h | 6 +++++-
> > virt/kvm/eventfd.c | 14 ++++++++++----
> > 4 files changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index 062cfd5..46f4b4d 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1946,6 +1946,11 @@ 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.
> >
> > +When KVM_CAP_IRQFD_IRQ_SOURCE_ID is available, KVM_IRQFD supports the
> > +KVM_IRQFD_FLAG_IRQ_SOURCE_ID which can be used to specify an IRQ
> > +source ID (see KVM_IRQ_SOURCE_ID) to be used for the guest interrupt.
> > +This flag has no effect on deassignment.
> > +
> > 4.76 KVM_PPC_ALLOCATE_HTAB
> >
> > Capability: KVM_CAP_PPC_ALLOC_HTAB
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 75e743e..946c5bd 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2174,6 +2174,7 @@ 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_IRQ_SOURCE_ID:
> > r = 1;
> > break;
> > case KVM_CAP_COALESCED_MMIO:
> > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > index 67b6b49..deda8a9 100644
> > --- a/include/linux/kvm.h
> > +++ b/include/linux/kvm.h
> > @@ -619,6 +619,7 @@ struct kvm_ppc_smmu_info {
> > #define KVM_CAP_S390_COW 79
> > #define KVM_CAP_PPC_ALLOC_HTAB 80
> > #define KVM_CAP_NR_IRQ_SOURCE_ID 81
> > +#define KVM_CAP_IRQFD_IRQ_SOURCE_ID 82
> >
> > #ifdef KVM_CAP_IRQ_ROUTING
> >
> > @@ -684,12 +685,15 @@ struct kvm_xen_hvm_config {
> > #endif
> >
> > #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
> > +/* Available with KVM_CAP_IRQFD_IRQ_SOURCE_ID */
> > +#define KVM_IRQFD_FLAG_IRQ_SOURCE_ID (1 << 1)
> >
> > struct kvm_irqfd {
> > __u32 fd;
> > __u32 gsi;
> > __u32 flags;
> > - __u8 pad[20];
> > + __u32 irq_source_id;
> > + __u8 pad[16];
> > };
> >
> > #define KVM_IRQ_SOURCE_ID_FLAG_DEASSIGN (1 << 0)
> > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> > index 7d7e2aa..30150f1 100644
> > --- a/virt/kvm/eventfd.c
> > +++ b/virt/kvm/eventfd.c
> > @@ -51,6 +51,7 @@ struct _irqfd {
> > struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
> > /* Used for level IRQ fast-path */
> > int gsi;
> > + int irq_source_id;
> > struct work_struct inject;
> > /* Used for setup/shutdown */
> > struct eventfd_ctx *eventfd;
> > @@ -67,8 +68,8 @@ irqfd_inject(struct work_struct *work)
> > struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
> > struct kvm *kvm = irqfd->kvm;
> >
> > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
> > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
> > + kvm_set_irq(kvm, irqfd->irq_source_id, irqfd->gsi, 1);
> > + kvm_set_irq(kvm, irqfd->irq_source_id, irqfd->gsi, 0);
>
> Looks like this can lead to kernel data corruption if irq_source_id
> specified it out of range?

Yep, we need range checking and maybe even cross check against user
allocated IDs.

> > }
> >
> > /*
> > @@ -138,7 +139,7 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
> > irq = rcu_dereference(irqfd->irq_entry);
> > /* An event has been signaled, inject an interrupt */
> > if (irq)
> > - kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
> > + kvm_set_msi(irq, kvm, irqfd->irq_source_id, 1);
> > else
> > schedule_work(&irqfd->inject);
> > rcu_read_unlock();
> > @@ -213,6 +214,10 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
> >
> > irqfd->kvm = kvm;
> > irqfd->gsi = args->gsi;
> > + if (args->flags & KVM_IRQFD_FLAG_IRQ_SOURCE_ID)
> > + irqfd->irq_source_id = args->irq_source_id;
> > + else
> > + irqfd->irq_source_id = KVM_USERSPACE_IRQ_SOURCE_ID;
>
> As in the previous patch, there is no validation
> that source id was previously allocated to userspace, so this makes life
> harder for userspace: if it deassigns a used source ID the result is not
> a clean failure but hard to find bugs.

Yep, good point. Some trivial bitmap management should fix this.

> > INIT_LIST_HEAD(&irqfd->list);
> > INIT_WORK(&irqfd->inject, irqfd_inject);
> > INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
> > @@ -340,7 +345,8 @@ 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_IRQ_SOURCE_ID))
> > return -EINVAL;
> >
> > if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)

Summary:
* user allocation bitmap needs to be cross-referenced by consumers
of user passed source IDs.

Thanks,

Alex