KVM: Allow host IRQ sharing for assigned PCI 2.3 devices

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@siemens.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 59a38264a0ed..6386f8c0482e 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1169,6 +1169,14 @@ 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.
@@ -1441,6 +1449,39 @@ The "num_dirty" field is a performance hint for KVM to determine whether it
 should skip processing the bitmap and just invalidate everything.  It must
 be set to the number of set bits in the bitmap.
 
+4.60 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
+
+Allows userspace to mask PCI INTx interrupts from the assigned device.  The
+kernel will not deliver INTx interrupts to the guest between setting and
+clearing of KVM_ASSIGN_SET_INTX_MASK via this interface.  This enables use of
+and emulation of PCI 2.3 INTx disable command register behavior.
+
+This may be used for both PCI 2.3 devices supporting INTx disable natively and
+older devices lacking this support. Userspace is responsible for emulating the
+read value of the INTx disable bit in the guest visible PCI command register.
+When modifying the INTx disable state, userspace should precede updating the
+physical device command register by calling this ioctl to inform the kernel of
+the new intended INTx mask state.
+
+Note that the kernel uses the device INTx disable bit to internally manage the
+device interrupt state for PCI 2.3 devices.  Reads of this register may
+therefore not match the expected value.  Writes should always use the guest
+intended INTx disable value rather than attempting to read-copy-update the
+current physical device state.  Races between user and kernel updates to the
+INTx disable bit are handled lazily in the kernel.  It's possible the device
+may generate unintended interrupts, but they will not be injected into the
+guest.
+
+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