Re: [PATCH 6/6] KVM: assigned dev: MSI-X mask support

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Nov 15, 2010 at 05:15:32PM +0800, Sheng Yang wrote:
> This patch enable per-vector mask for assigned devices using MSI-X.
> 
> This patch provided two new APIs: one is for guest to specific device's MSI-X
> table address in MMIO, the other is for userspace to get information about mask
> bit.
> 
> All the mask bit operation are kept in kernel, in order to accelerate.
> Userspace shouldn't access the device MMIO directly for the information,
> instead it should uses provided API to do so.
> 
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>
> ---
>  arch/x86/kvm/x86.c       |    1 +
>  include/linux/kvm.h      |   32 +++++
>  include/linux/kvm_host.h |    5 +
>  virt/kvm/assigned-dev.c  |  318 +++++++++++++++++++++++++++++++++++++++++++++-
>  4 files changed, 355 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fc29223..37602e2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1966,6 +1966,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_X86_ROBUST_SINGLESTEP:
>  	case KVM_CAP_XSAVE:
>  	case KVM_CAP_ASYNC_PF:
> +	case KVM_CAP_MSIX_MASK:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index ea2dc1a..b3e5ffe 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -541,6 +541,9 @@ struct kvm_ppc_pvinfo {
>  #define KVM_CAP_PPC_GET_PVINFO 57
>  #define KVM_CAP_PPC_IRQ_LEVEL 58
>  #define KVM_CAP_ASYNC_PF 59
> +#ifdef __KVM_HAVE_MSIX
> +#define KVM_CAP_MSIX_MASK 60
> +#endif
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -672,6 +675,9 @@ struct kvm_clock_data {
>  #define KVM_XEN_HVM_CONFIG        _IOW(KVMIO,  0x7a, struct kvm_xen_hvm_config)
>  #define KVM_SET_CLOCK             _IOW(KVMIO,  0x7b, struct kvm_clock_data)
>  #define KVM_GET_CLOCK             _IOR(KVMIO,  0x7c, struct kvm_clock_data)
> +/* Available with KVM_CAP_MSIX_MASK */
> +#define KVM_GET_MSIX_ENTRY        _IOWR(KVMIO,  0x7d, struct kvm_msix_entry)
> +#define KVM_UPDATE_MSIX_MMIO      _IOW(KVMIO,  0x7e, struct kvm_msix_mmio)
>  /* Available with KVM_CAP_PIT_STATE2 */
>  #define KVM_GET_PIT2              _IOR(KVMIO,  0x9f, struct kvm_pit_state2)
>  #define KVM_SET_PIT2              _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
> @@ -795,4 +801,30 @@ struct kvm_assigned_msix_entry {
>  	__u16 padding[3];
>  };
>  
> +#define KVM_MSIX_TYPE_ASSIGNED_DEV	1
> +
> +#define KVM_MSIX_FLAG_MASKBIT		(1 << 0)
> +#define KVM_MSIX_FLAG_QUERY_MASKBIT	(1 << 0)
> +
> +struct kvm_msix_entry {
> +	__u32 id;
> +	__u32 type;

Is type really necessary? Will it ever differ from
KVM_MSIX_TYPE_ASSIGNED_DEV?

> +	__u32 entry; /* The index of entry in the MSI-X table */
> +	__u32 flags;
> +	__u32 query_flags;
> +	__u32 reserved[5];
> +};
> +
> +#define KVM_MSIX_MMIO_FLAG_REGISTER	(1 << 0)
> +#define KVM_MSIX_MMIO_FLAG_UNREGISTER	(1 << 1)
> +
> +struct kvm_msix_mmio {
> +	__u32 id;
> +	__u32 type;
> +	__u64 base_addr;
> +	__u32 max_entries_nr;
> +	__u32 flags;
> +	__u32 reserved[6];
> +};
> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f09db87..57a437a 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -501,6 +501,7 @@ struct kvm_guest_msix_entry {
>  };
>  
>  #define KVM_ASSIGNED_ENABLED_IOMMU		(1 << 0)
> +#define KVM_ASSIGNED_ENABLED_MSIX_MMIO		(1 << 1)
>  struct kvm_assigned_dev_kernel {
>  	struct kvm_irq_ack_notifier ack_notifier;
>  	struct work_struct interrupt_work;
> @@ -521,6 +522,10 @@ struct kvm_assigned_dev_kernel {
>  	struct pci_dev *dev;
>  	struct kvm *kvm;
>  	spinlock_t assigned_dev_lock;
> +	DECLARE_BITMAP(msix_mask_bitmap, KVM_MAX_MSIX_PER_DEV);
> +	gpa_t msix_mmio_base;
> +	struct kvm_io_device msix_mmio_dev;
> +	int msix_max_entries_nr;
>  };
>  
>  struct kvm_irq_mask_notifier {
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index 5c6b96d..76a1f12 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -226,12 +226,27 @@ static void kvm_free_assigned_irq(struct kvm *kvm,
>  	kvm_deassign_irq(kvm, assigned_dev, assigned_dev->irq_requested_type);
>  }
>  
> +static void unregister_msix_mmio(struct kvm *kvm,
> +				 struct kvm_assigned_dev_kernel *adev)
> +{
> +	if (adev->flags & KVM_ASSIGNED_ENABLED_MSIX_MMIO) {
> +		mutex_lock(&kvm->slots_lock);
> +		kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS,
> +				&adev->msix_mmio_dev);
> +		mutex_unlock(&kvm->slots_lock);
> +		adev->flags &= ~KVM_ASSIGNED_ENABLED_MSIX_MMIO;
> +	}
> +}
> +
>  static void kvm_free_assigned_device(struct kvm *kvm,
>  				     struct kvm_assigned_dev_kernel
>  				     *assigned_dev)
>  {
>  	kvm_free_assigned_irq(kvm, assigned_dev);
>  
> +#ifdef __KVM_HAVE_MSIX
> +	unregister_msix_mmio(kvm, assigned_dev);
> +#endif
>  	pci_reset_function(assigned_dev->dev);
>  
>  	pci_release_regions(assigned_dev->dev);
> @@ -504,7 +519,7 @@ out:
>  static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
>  				      struct kvm_assigned_pci_dev *assigned_dev)
>  {
> -	int r = 0, idx;
> +	int r = 0, idx, i;
>  	struct kvm_assigned_dev_kernel *match;
>  	struct pci_dev *dev;
>  
> @@ -564,6 +579,10 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
>  
>  	list_add(&match->list, &kvm->arch.assigned_dev_head);
>  
> +	/* The state after reset of MSI-X table is all masked */
> +	for (i = 0; i < KVM_MAX_MSIX_PER_DEV; i++)
> +		set_bit(i, match->msix_mask_bitmap);
> +
>  	if (assigned_dev->flags & KVM_ASSIGNED_ENABLED_IOMMU) {
>  		if (!kvm->arch.iommu_domain) {
>  			r = kvm_iommu_map_guest(kvm);
> @@ -667,6 +686,43 @@ msix_nr_out:
>  	return r;
>  }
>  
> +static void update_msix_mask(struct kvm_assigned_dev_kernel *adev,
> +			     int idx, bool new_mask_flag)
> +{
> +	int irq;
> +	bool old_mask_flag, need_flush = false;
> +
> +	spin_lock_irq(&adev->assigned_dev_lock);
> +
> +	if (!adev->dev->msix_enabled ||
> +	    !(adev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX))
> +		goto out;
> +
> +	old_mask_flag = test_bit(adev->guest_msix_entries[idx].entry,
> +			adev->msix_mask_bitmap);
> +	if (old_mask_flag == new_mask_flag)
> +		goto out;
> +
> +	irq = adev->host_msix_entries[idx].vector;
> +	BUG_ON(irq == 0);
> +
> +	if (new_mask_flag) {
> +		set_bit(adev->guest_msix_entries[idx].entry,
> +				adev->msix_mask_bitmap);
> +		disable_irq_nosync(irq);
> +		need_flush = true;
> +	} else {
> +		clear_bit(adev->guest_msix_entries[idx].entry,
> +				adev->msix_mask_bitmap);
> +		enable_irq(irq);
> +	}
> +out:
> +	spin_unlock_irq(&adev->assigned_dev_lock);
> +
> +	if (need_flush)
> +		flush_work(&adev->interrupt_work);
> +}
> +
>  static int kvm_vm_ioctl_set_msix_entry(struct kvm *kvm,
>  				       struct kvm_assigned_msix_entry *entry)
>  {
> @@ -701,6 +757,235 @@ msix_entry_out:
>  
>  	return r;
>  }
> +
> +static int kvm_vm_ioctl_get_msix_entry(struct kvm *kvm,
> +				       struct kvm_msix_entry *entry)
> +{
> +	int r = 0;
> +	struct kvm_assigned_dev_kernel *adev;
> +
> +	if (entry->type != KVM_MSIX_TYPE_ASSIGNED_DEV)
> +		return -EINVAL;
> +
> +	if (!entry->query_flags)
> +		return -EINVAL;
> +
> +	mutex_lock(&kvm->lock);
> +
> +	adev = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
> +				      entry->id);
> +
> +	if (!adev) {
> +		r = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (entry->entry >= adev->msix_max_entries_nr) {
> +		r = -ENOSPC;
> +		goto out;
> +	}
> +
> +	if (entry->query_flags & KVM_MSIX_FLAG_QUERY_MASKBIT) {
> +		if (test_bit(entry->entry, adev->msix_mask_bitmap))
> +			entry->flags |= KVM_MSIX_FLAG_MASKBIT;
> +		else
> +			entry->flags &= ~KVM_MSIX_FLAG_MASKBIT;
> +	}
> +
> +out:
> +	mutex_unlock(&kvm->lock);
> +
> +	return r;
> +}
> +
> +static bool msix_mmio_in_range(struct kvm_assigned_dev_kernel *adev,
> +			      gpa_t addr, int len)
> +{
> +	gpa_t start, end;
> +
> +	BUG_ON(!(adev->flags & KVM_ASSIGNED_ENABLED_MSIX_MMIO));
> +	start = adev->msix_mmio_base;
> +	end = adev->msix_mmio_base + PCI_MSIX_ENTRY_SIZE *
> +		adev->msix_max_entries_nr;
> +	if (addr >= start && addr + len <= end)
> +		return true;
> +
> +	return false;
> +}
> +
> +static int msix_get_enabled_idx(struct kvm_assigned_dev_kernel *adev,
> +			      gpa_t addr, int len)
> +{
> +	int i, index = (addr - adev->msix_mmio_base) / PCI_MSIX_ENTRY_SIZE;
> +
> +	for (i = 0; i < adev->entries_nr; i++)
> +		if (adev->guest_msix_entries[i].entry == index)
> +			return i;
> +
> +	return -EINVAL;
> +}
> +
> +static int msix_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
> +			  void *val)
> +{
> +	struct kvm_assigned_dev_kernel *adev =
> +			container_of(this, struct kvm_assigned_dev_kernel,
> +				     msix_mmio_dev);
> +	int idx, r = 0;
> +	u32 entry[4];
> +	struct kvm_kernel_irq_routing_entry e;
> +
> +	/* TODO: Get big-endian machine work */
> +	mutex_lock(&adev->kvm->lock);
> +	if (!msix_mmio_in_range(adev, addr, len)) {
> +		r = -EOPNOTSUPP;
> +		goto out;
> +	}

The unregister path does:

mutex_lock(kvm->lock)
kvm_io_bus_unregister_dev()
synchronize_srcu()

If an instance of msix_mmio_read/msix_mmio_write is waiting on
kvm->lock, synchronize_srcu will never complete.

You should use a separate lock for the in range check (and have it mind
that reads/writes can trigger after kvm_io_bus_register_dev, so all
state accessible in the r/w handlers should be complete by that time).

> +	if ((addr & 0x3) || len != 4)
> +		goto out;
> +
> +	idx = msix_get_enabled_idx(adev, addr, len);
> +	if (idx < 0) {
> +		idx = (addr - adev->msix_mmio_base) / PCI_MSIX_ENTRY_SIZE;
> +		if ((addr % PCI_MSIX_ENTRY_SIZE) ==
> +				PCI_MSIX_ENTRY_VECTOR_CTRL)
> +			*(unsigned long *)val =
> +				test_bit(idx, adev->msix_mask_bitmap) ?
> +				PCI_MSIX_ENTRY_CTRL_MASKBIT : 0;
> +		else
> +			r = -EOPNOTSUPP;
> +		goto out;
> +	}
> +
> +	r = kvm_get_irq_routing_entry(adev->kvm,
> +			adev->guest_msix_entries[idx].vector, &e);
> +	if (r || e.type != KVM_IRQ_ROUTING_MSI) {
> +		r = -EOPNOTSUPP;
> +		goto out;
> +	}
> +	entry[0] = e.msi.address_lo;
> +	entry[1] = e.msi.address_hi;
> +	entry[2] = e.msi.data;
> +	entry[3] = test_bit(adev->guest_msix_entries[idx].entry,
> +			adev->msix_mask_bitmap);
> +	memcpy(val, &entry[addr % PCI_MSIX_ENTRY_SIZE / sizeof *entry], len);

Division by zero?