On Mon, Jan 09, 2012 at 03:03:00PM +0100, Jan Kiszka wrote:
> PCI 2.3 allows to generically disable IRQ sources at device level. This
> enables us to share legacy IRQs of such devices with other host devices
> when passing them to a guest.
>
> The new IRQ sharing feature introduced here is optional, user space has
> to request it explicitly. Moreover, user space can inform us about its
> view of PCI_COMMAND_INTX_DISABLE so that we can avoid unmasking the
> interrupt and signaling it if the guest masked it via the virtualized
> PCI config space.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
>
> This applies to kvm/master after merging
>
> PCI: Rework config space blocking services
> PCI: Introduce INTx check & mask API
>
> from current linux-next/master. I suppose those two will make it into
> 3.3.
>
> To recall the history of it: I tried hard to implement an adaptive
> solution that automatically picks the fastest masking technique whenever
> possible. However, the changes required to the IRQ core subsystem and
> the logic of the device assignment code became so complex and partly
> ugly that I gave up on this. It's simply not worth the pain given that
> legacy PCI interrupts are rarely raised for performance critical device
> at such a high rate (KHz...) that you can measure the difference.
>
> Documentation/virtual/kvm/api.txt | 27 +++++
> arch/x86/kvm/x86.c | 1 +
> include/linux/kvm.h | 6 +
> include/linux/kvm_host.h | 2 +
> virt/kvm/assigned-dev.c | 208 +++++++++++++++++++++++++++++++-----
> 5 files changed, 215 insertions(+), 29 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index e1d94bf..670015a 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1159,6 +1159,14 @@ following flags are specified:
>
> /* Depends on KVM_CAP_IOMMU */
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> +/* The following two depend on KVM_CAP_PCI_2_3 */
> +#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> +#define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)
> +
> +If KVM_DEV_ASSIGN_PCI_2_3 is set, the kernel will manage legacy INTx interrupts
> +via the PCI-2.3-compliant device-level mask, thus enable IRQ sharing with other
> +assigned devices or host devices. KVM_DEV_ASSIGN_MASK_INTX specifies the
> +guest's view on the INTx mask, see KVM_ASSIGN_SET_INTX_MASK for details.
>
> The KVM_DEV_ASSIGN_ENABLE_IOMMU flag is a mandatory option to ensure
> isolation of the device. Usages not specifying this flag are deprecated.
> @@ -1399,6 +1407,25 @@ The following flags are defined:
> If datamatch flag is set, the event will be signaled only if the written value
> to the registered address is equal to datamatch in struct kvm_ioeventfd.
>
> +4.59 KVM_ASSIGN_SET_INTX_MASK
> +
> +Capability: KVM_CAP_PCI_2_3
> +Architectures: x86
> +Type: vm ioctl
> +Parameters: struct kvm_assigned_pci_dev (in)
> +Returns: 0 on success, -1 on error
> +
> +Informs the kernel about the guest's view on the INTx mask.
A wild idea: since this is guest view of its IRQ,
can this be specified per guest IRQ+id then?
That might be useful to support MSIX mask bit emulation.
> As long as the
> +guest masks the legacy INTx, the kernel will refrain from unmasking it at
> +hardware level and will not assert the guest's IRQ line. User space is still
> +responsible for applying this state to the assigned device's real config space.
Can this be made more explicit? You mean writing into 1st
byte of PCI control, right?
> +To avoid that the kernel overwrites the state user space wants to set,
> +KVM_ASSIGN_SET_INTX_MASK has to be called prior to updating the config space.
This looks like a strange requirement, could you explain how
this helps avoid races? This also raises questions about
what should be done to write a bit unrelated to masking.
> +
> +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.
> +
> 4.62 KVM_CREATE_SPAPR_TCE
>
> Capability: KVM_CAP_SPAPR_TCE
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1171def..9381806 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2057,6 +2057,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> case KVM_CAP_XSAVE:
> case KVM_CAP_ASYNC_PF:
> case KVM_CAP_GET_TSC_KHZ:
> + case KVM_CAP_PCI_2_3:
> r = 1;
> break;
> case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 68e67e5..da5f7b7 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -556,6 +556,7 @@ struct kvm_ppc_pvinfo {
> #define KVM_CAP_PPC_RMA 65
> #define KVM_CAP_MAX_VCPUS 66 /* returns max vcpus per vm */
> #define KVM_CAP_PPC_PAPR 68
> +#define KVM_CAP_PCI_2_3 69
> #define KVM_CAP_S390_GMAP 71
> #define KVM_CAP_TSC_DEADLINE_TIMER 72
>
> @@ -697,6 +698,9 @@ struct kvm_clock_data {
> /* Available with KVM_CAP_TSC_CONTROL */
> #define KVM_SET_TSC_KHZ _IO(KVMIO, 0xa2)
> #define KVM_GET_TSC_KHZ _IO(KVMIO, 0xa3)
> +/* Available with KVM_CAP_PCI_2_3 */
> +#define KVM_ASSIGN_SET_INTX_MASK _IOW(KVMIO, 0xa4, \
> + struct kvm_assigned_pci_dev)
>
> /*
> * ioctls for vcpu fds
> @@ -765,6 +769,8 @@ struct kvm_clock_data {
> #define KVM_ALLOCATE_RMA _IOR(KVMIO, 0xa9, struct kvm_allocate_rma)
>
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> +#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> +#define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)
>
> struct kvm_assigned_pci_dev {
> __u32 assigned_dev_id;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 900c763..07461bd 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -546,6 +546,7 @@ struct kvm_assigned_dev_kernel {
> unsigned int entries_nr;
> int host_irq;
> bool host_irq_disabled;
> + bool pci_2_3;
> struct msix_entry *host_msix_entries;
> int guest_irq;
> struct msix_entry *guest_msix_entries;
> @@ -555,6 +556,7 @@ struct kvm_assigned_dev_kernel {
> struct pci_dev *dev;
> struct kvm *kvm;
> spinlock_t intx_lock;
> + struct mutex intx_mask_lock;
What exactly does this lock protect?
I see it used sometimes with intx_lock and sometimes without.
> char irq_name[32];
> struct pci_saved_state *pci_saved_state;
> };
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index 758e3b3..b35aba9 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -57,22 +57,66 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
> return index;
> }
>
> -static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
> +static irqreturn_t kvm_assigned_dev_intx(int irq, void *dev_id)
> {
> struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> + int ret;
>
> - if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_INTX) {
> - spin_lock(&assigned_dev->intx_lock);
> + spin_lock(&assigned_dev->intx_lock);
> + if (pci_check_and_mask_intx(assigned_dev->dev)) {
> + assigned_dev->host_irq_disabled = true;
> + ret = IRQ_WAKE_THREAD;
> + } else
> + ret = IRQ_NONE;
> + spin_unlock(&assigned_dev->intx_lock);
> +
> + return ret;
> +}
> +
> +static void
> +kvm_assigned_dev_raise_guest_irq(struct kvm_assigned_dev_kernel *assigned_dev,
> + int vector)
> +{
> + if (unlikely(assigned_dev->irq_requested_type &
> + KVM_DEV_IRQ_GUEST_INTX)) {
> + mutex_lock(&assigned_dev->intx_mask_lock);
> + if (!(assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX))
> + kvm_set_irq(assigned_dev->kvm,
> + assigned_dev->irq_source_id, vector, 1);
> + mutex_unlock(&assigned_dev->intx_mask_lock);
> + } else
> + kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
> + vector, 1);
> +}
> +
> +static irqreturn_t kvm_assigned_dev_thread_intx(int irq, void *dev_id)
> +{
> + struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> +
> + if (!(assigned_dev->flags & KVM_DEV_ASSIGN_PCI_2_3)) {
> + spin_lock_irq(&assigned_dev->intx_lock);
> disable_irq_nosync(irq);
> assigned_dev->host_irq_disabled = true;
> - spin_unlock(&assigned_dev->intx_lock);
> + spin_unlock_irq(&assigned_dev->intx_lock);
> }
>
> - kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
> - assigned_dev->guest_irq, 1);
> + kvm_assigned_dev_raise_guest_irq(assigned_dev,
> + assigned_dev->guest_irq);
> +
> + return IRQ_HANDLED;
> +}
> +
> +#ifdef __KVM_HAVE_MSI
> +static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id)
> +{
> + struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> +
> + kvm_assigned_dev_raise_guest_irq(assigned_dev,
> + assigned_dev->guest_irq);
>
> return IRQ_HANDLED;
> }
> +#endif
>
> #ifdef __KVM_HAVE_MSIX
> static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
> @@ -83,8 +127,7 @@ static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
>
> if (index >= 0) {
> vector = assigned_dev->guest_msix_entries[index].vector;
> - kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
> - vector, 1);
> + kvm_assigned_dev_raise_guest_irq(assigned_dev, vector);
> }
>
> return IRQ_HANDLED;
> @@ -100,15 +143,31 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
>
> kvm_set_irq(dev->kvm, dev->irq_source_id, dev->guest_irq, 0);
>
> - /* The guest irq may be shared so this ack may be
> - * from another device.
> - */
> - spin_lock(&dev->intx_lock);
> - if (dev->host_irq_disabled) {
> - enable_irq(dev->host_irq);
> - dev->host_irq_disabled = false;
> + mutex_lock(&dev->intx_mask_lock);
> +
> + if (!(dev->flags & KVM_DEV_ASSIGN_MASK_INTX)) {
> + bool reassert = false;
> +
> + spin_lock_irq(&dev->intx_lock);
> + /*
> + * The guest IRQ may be shared so this ack can come from an
> + * IRQ for another guest device.
> + */
> + if (dev->host_irq_disabled) {
> + if (!(dev->flags & KVM_DEV_ASSIGN_PCI_2_3))
> + enable_irq(dev->host_irq);
> + else if (!pci_check_and_unmask_intx(dev->dev))
> + reassert = true;
> + dev->host_irq_disabled = reassert;
> + }
> + spin_unlock_irq(&dev->intx_lock);
> +
> + if (reassert)
> + kvm_set_irq(dev->kvm, dev->irq_source_id,
> + dev->guest_irq, 1);
> }
> - spin_unlock(&dev->intx_lock);
> +
> + mutex_unlock(&dev->intx_mask_lock);
> }
>
> static void deassign_guest_irq(struct kvm *kvm,
> @@ -156,7 +215,13 @@ static void deassign_host_irq(struct kvm *kvm,
> pci_disable_msix(assigned_dev->dev);
> } else {
> /* Deal with MSI and INTx */
> - disable_irq(assigned_dev->host_irq);
> + if (assigned_dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
> + spin_lock_irq(&assigned_dev->intx_lock);
Interesting that the new mutex is not used here.
> + pci_intx(assigned_dev->dev, false);
Interesting.
This will leave the device with interrupts masked.
Do we reset it later?
Maybe we want a comment explaining why it's done.
> + spin_unlock_irq(&assigned_dev->intx_lock);
> + synchronize_irq(assigned_dev->host_irq);
> + } else
> + disable_irq(assigned_dev->host_irq);
>
> free_irq(assigned_dev->host_irq, assigned_dev);
>
> @@ -237,15 +302,34 @@ void kvm_free_all_assigned_devices(struct kvm *kvm)
> static int assigned_device_enable_host_intx(struct kvm *kvm,
> struct kvm_assigned_dev_kernel *dev)
> {
> + irq_handler_t irq_handler;
> + unsigned long flags;
> +
> dev->host_irq = dev->dev->irq;
> - /* Even though this is PCI, we don't want to use shared
> - * interrupts. Sharing host devices with guest-assigned devices
> - * on the same interrupt line is not a happy situation: there
> - * are going to be long delays in accepting, acking, etc.
> +
> + /*
> + * We can only share the IRQ line with other host devices if we are
> + * able to disable the IRQ source at device-level - independently of
> + * the guest driver. Otherwise host devices may suffer from unbounded
> + * IRQ latencies when the guest keeps the line asserted.
> */
> - if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> - IRQF_ONESHOT, dev->irq_name, dev))
> + if (dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
> + irq_handler = kvm_assigned_dev_intx;
> + flags = IRQF_SHARED;
> + } else {
> + irq_handler = NULL;
> + flags = IRQF_ONESHOT;
> + }
> + if (request_threaded_irq(dev->host_irq, irq_handler,
> + kvm_assigned_dev_thread_intx, flags,
> + dev->irq_name, dev))
> return -EIO;
> +
> + if (dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
> + spin_lock_irq(&dev->intx_lock);
> + pci_intx(dev->dev, true);
> + spin_unlock_irq(&dev->intx_lock);
> + }
> return 0;
> }
>
> @@ -262,8 +346,9 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
> }
>
> dev->host_irq = dev->dev->irq;
> - if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> - 0, dev->irq_name, dev)) {
> + if (request_threaded_irq(dev->host_irq, NULL,
> + kvm_assigned_dev_thread_msi, 0,
> + dev->irq_name, dev)) {
> pci_disable_msi(dev->dev);
> return -EIO;
> }
> @@ -321,7 +406,6 @@ static int assigned_device_enable_guest_msi(struct kvm *kvm,
> {
> dev->guest_irq = irq->guest_irq;
> dev->ack_notifier.gsi = -1;
> - dev->host_irq_disabled = false;
> return 0;
> }
> #endif
> @@ -333,7 +417,6 @@ static int assigned_device_enable_guest_msix(struct kvm *kvm,
> {
> dev->guest_irq = irq->guest_irq;
> dev->ack_notifier.gsi = -1;
> - dev->host_irq_disabled = false;
> return 0;
> }
> #endif
> @@ -367,6 +450,7 @@ static int assign_host_irq(struct kvm *kvm,
> default:
> r = -EINVAL;
> }
> + dev->host_irq_disabled = false;
>
> if (!r)
> dev->irq_requested_type |= host_irq_type;
> @@ -468,6 +552,7 @@ static int kvm_vm_ioctl_deassign_dev_irq(struct kvm *kvm,
> {
> int r = -ENODEV;
> struct kvm_assigned_dev_kernel *match;
> + unsigned long irq_type;
>
> mutex_lock(&kvm->lock);
>
> @@ -476,7 +561,9 @@ static int kvm_vm_ioctl_deassign_dev_irq(struct kvm *kvm,
> if (!match)
> goto out;
>
> - r = kvm_deassign_irq(kvm, match, assigned_irq->flags);
> + irq_type = assigned_irq->flags & (KVM_DEV_IRQ_HOST_MASK |
> + KVM_DEV_IRQ_GUEST_MASK);
> + r = kvm_deassign_irq(kvm, match, irq_type);
> out:
> mutex_unlock(&kvm->lock);
> return r;
> @@ -609,6 +696,10 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
> if (!match->pci_saved_state)
> printk(KERN_DEBUG "%s: Couldn't store %s saved state\n",
> __func__, dev_name(&dev->dev));
> +
> + if (!pci_intx_mask_supported(dev))
> + assigned_dev->flags &= ~KVM_DEV_ASSIGN_PCI_2_3;
> +
> match->assigned_dev_id = assigned_dev->assigned_dev_id;
> match->host_segnr = assigned_dev->segnr;
> match->host_busnr = assigned_dev->busnr;
> @@ -616,6 +707,7 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
> match->flags = assigned_dev->flags;
> match->dev = dev;
> spin_lock_init(&match->intx_lock);
> + mutex_init(&match->intx_mask_lock);
> match->irq_source_id = -1;
> match->kvm = kvm;
> match->ack_notifier.irq_acked = kvm_assigned_dev_ack_irq;
> @@ -761,6 +853,56 @@ msix_entry_out:
> }
> #endif
>
> +static int kvm_vm_ioctl_set_pci_irq_mask(struct kvm *kvm,
> + struct kvm_assigned_pci_dev *assigned_dev)
> +{
> + int r = 0;
> + struct kvm_assigned_dev_kernel *match;
> +
> + mutex_lock(&kvm->lock);
> +
> + match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
> + assigned_dev->assigned_dev_id);
> + if (!match) {
> + r = -ENODEV;
> + goto out;
> + }
> +
> + mutex_lock(&match->intx_mask_lock);
> +
> + match->flags &= ~KVM_DEV_ASSIGN_MASK_INTX;
> + match->flags |= assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX;
> +
> + if (match->irq_requested_type & KVM_DEV_IRQ_GUEST_INTX) {
> + if (assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX) {
> + kvm_set_irq(match->kvm, match->irq_source_id,
> + match->guest_irq, 0);
> + /*
> + * Masking at hardware-level is performed on demand,
> + * i.e. when an IRQ actually arrives at the host.
> + */
> + } else {
> + /*
> + * Unmask the IRQ line. It may have been masked
> + * meanwhile if we aren't using PCI 2.3 INTx masking
> + * on the host side.
> + */
> + spin_lock_irq(&match->intx_lock);
> + if (match->host_irq_disabled) {
> + enable_irq(match->host_irq);
> + match->host_irq_disabled = false;
> + }
> + spin_unlock_irq(&match->intx_lock);
> + }
> + }
> +
> + mutex_unlock(&match->intx_mask_lock);
> +
> +out:
> + mutex_unlock(&kvm->lock);
> + return r;
> +}
> +
> long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
> unsigned long arg)
> {
> @@ -868,6 +1010,15 @@ long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
> break;
> }
> #endif
> + case KVM_ASSIGN_SET_INTX_MASK: {
> + struct kvm_assigned_pci_dev assigned_dev;
> +
> + r = -EFAULT;
> + if (copy_from_user(&assigned_dev, argp, sizeof assigned_dev))
> + goto out;
> + r = kvm_vm_ioctl_set_pci_irq_mask(kvm, &assigned_dev);
> + break;
> + }
> default:
> r = -ENOTTY;
> break;
> @@ -875,4 +1026,3 @@ long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
> out:
> return r;
> }
> -
> --
> 1.7.3.4
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