Re: [PATCH v4] KVM: Introduce direct MSI message injection for in-kernel irqchips

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 29, 2012 at 09:14:12PM +0200, Jan Kiszka wrote:
> Currently, MSI messages can only be injected to in-kernel irqchips by
> defining a corresponding IRQ route for each message. This is not only
> unhandy if the MSI messages are generated "on the fly" by user space,
> IRQ routes are a limited resource that user space has to manage
> carefully.
> 
> By providing a direct injection path, we can both avoid using up limited
> resources and simplify the necessary steps for user land.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Changes in v4:
>  - Fix the build by factoring out kvm_send_userspace_msi:
>    irqchip_in_kernel is not generically available. But abstracting it
>    for all arch is tricky and therefore left to the poor people who have
>    to introduce non-x86 irqchip support to this x86-focused corner.
> 
> Lesson (probably not) learned: Never underestimate the complexity of
> trivial changes.
> 
>  Documentation/virtual/kvm/api.txt |   21 +++++++++++++++++++++
>  arch/x86/kvm/Kconfig              |    1 +
>  include/linux/kvm.h               |   11 +++++++++++
>  include/linux/kvm_host.h          |    2 ++
>  virt/kvm/Kconfig                  |    3 +++
>  virt/kvm/irq_comm.c               |   14 ++++++++++++++
>  virt/kvm/kvm_main.c               |   14 ++++++++++++++
>  7 files changed, 66 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 81ff39f..ed27d1b 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1482,6 +1482,27 @@ See KVM_ASSIGN_DEV_IRQ for the data structure.  The target device is specified
>  by assigned_dev_id.  In the flags field, only KVM_DEV_ASSIGN_MASK_INTX is
>  evaluated.
>  
> +4.61 KVM_SIGNAL_MSI
> +
> +Capability: KVM_CAP_SIGNAL_MSI
> +Architectures: x86
> +Type: vm ioctl
> +Parameters: struct kvm_msi (in)
> +Returns: >0 on delivery, 0 if guest blocked the MSI, and -1 on error
> +
> +Directly inject a MSI message. Only valid with in-kernel irqchip that handles
> +MSI messages.
> +
> +struct kvm_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 flags;
> +	__u8  pad[16];
> +};
> +
> +No flags are defined so far. The corresponding field must be 0.
> +
>  4.62 KVM_CREATE_SPAPR_TCE
>  
>  Capability: KVM_CAP_SPAPR_TCE
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 1a7fe86..a28f338 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -36,6 +36,7 @@ config KVM
>  	select TASKSTATS
>  	select TASK_DELAY_ACCT
>  	select PERF_EVENTS
> +	select HAVE_KVM_MSI
>  	---help---
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 7a9dd4b..225b452 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -590,6 +590,7 @@ struct kvm_ppc_pvinfo {
>  #define KVM_CAP_SYNC_REGS 74
>  #define KVM_CAP_PCI_2_3 75
>  #define KVM_CAP_KVMCLOCK_CTRL 76
> +#define KVM_CAP_SIGNAL_MSI 77
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -715,6 +716,14 @@ struct kvm_one_reg {
>  	__u64 addr;
>  };
>  
> +struct kvm_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 flags;
> +	__u8  pad[16];
> +};
> +
>  /*
>   * ioctls for VM fds
>   */
> @@ -789,6 +798,8 @@ struct kvm_s390_ucas_mapping {
>  /* Available with KVM_CAP_PCI_2_3 */
>  #define KVM_ASSIGN_SET_INTX_MASK  _IOW(KVMIO,  0xa4, \
>  				       struct kvm_assigned_pci_dev)
> +/* Available with KVM_CAP_SIGNAL_MSI */
> +#define KVM_SIGNAL_MSI            _IOW(KVMIO,  0xa5, struct kvm_msi)
>  
>  /*
>   * ioctls for vcpu fds
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6cf158c..35c69d6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -774,6 +774,8 @@ int kvm_set_irq_routing(struct kvm *kvm,
>  			unsigned flags);
>  void kvm_free_irq_routing(struct kvm *kvm);
>  
> +int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi);
> +
>  #else
>  
>  static inline void kvm_free_irq_routing(struct kvm *kvm) {}
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index f63ccb0..28694f4 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -18,3 +18,6 @@ config KVM_MMIO
>  
>  config KVM_ASYNC_PF
>         bool
> +
> +config HAVE_KVM_MSI
> +       bool
> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> index 9f614b4..a6a0365 100644
> --- a/virt/kvm/irq_comm.c
> +++ b/virt/kvm/irq_comm.c
> @@ -138,6 +138,20 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
>  	return kvm_irq_delivery_to_apic(kvm, NULL, &irq);
>  }
>  
> +int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi)
> +{
> +	struct kvm_kernel_irq_routing_entry route;
> +
> +	if (!irqchip_in_kernel(kvm) || msi->flags != 0)
> +		return -EINVAL;
> +
> +	route.msi.address_lo = msi->address_lo;
> +	route.msi.address_hi = msi->address_hi;
> +	route.msi.data = msi->data;
> +
> +	return kvm_set_msi(&route, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
> +}
> +
>  /*
>   * Return value:
>   *  < 0   Interrupt was ignored (masked or not delivered for other reasons)
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a612bc8..5addfa8 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2063,6 +2063,17 @@ static long kvm_vm_ioctl(struct file *filp,
>  		mutex_unlock(&kvm->lock);
>  		break;
>  #endif
> +#ifdef CONFIG_HAVE_KVM_MSI
> +	case KVM_SIGNAL_MSI: {
> +		struct kvm_msi msi;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&msi, argp, sizeof msi))
> +			goto out;

Wait a second, we should validate flags: you say
"this field should be 0" so we should check it.

> +		r = kvm_send_userspace_msi(kvm, &msi);
> +		break;
> +	}
> +#endif
>  	default:
>  		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
>  		if (r == -ENOTTY)
> @@ -2191,6 +2202,9 @@ static long kvm_dev_ioctl_check_extension_generic(long arg)
>  	case KVM_CAP_SET_BOOT_CPU_ID:
>  #endif
>  	case KVM_CAP_INTERNAL_ERROR_DATA:
> +#ifdef CONFIG_HAVE_KVM_MSI
> +	case KVM_CAP_SIGNAL_MSI:
> +#endif
>  		return 1;
>  #ifdef CONFIG_HAVE_KVM_IRQCHIP
>  	case KVM_CAP_IRQ_ROUTING:
> -- 
> 1.7.3.4