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

Michael S. Tsirkin
2012-08-15T13:48:19Z

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?

> }
>
> /*
> @@ -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.

> 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)