[RFC PATCH 5/8] vfio/pci: Remove interrupt context counter

[Reinette Chatre]

struct vfio_pci_core_device::num_ctx counts how many interrupt
contexts have been allocated. When all interrupt contexts are
allocated simultaneously num_ctx provides the upper bound of all
vectors that can be used as indices into the interrupt context
array.

With the upcoming support for dynamic MSI-X the number of
interrupt contexts does not necessarily span the range of allocated
interrupts. Consequently, num_ctx is no longer a trusted upper bound
for valid indices.

Stop using num_ctx to determine if a provided vector is valid, use
the existence of interrupt context directly.

Introduce a helper that ensures a provided interrupt range is
allocated before any user requested action is taken. This maintains
existing behavior (early exit without modifications) when user
space attempts to modify a range of vectors that includes unallocated
interrupts.

The checks that ensure that user space provides a range of vectors
that is valid for the device are untouched.

Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
---

Existing behavior on error paths is not maintained for MSI-X
when adding support for dynamic MSI-X. Please see maintainer
comments associated with "vfio/pci: Support dynamic MSI-x".

 drivers/vfio/pci/vfio_pci_intrs.c | 30 ++++++++++++++++++++----------
 include/linux/vfio_pci_core.h     |  1 -
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index bfcf5cb6b435..187a1ba34a16 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -107,6 +107,21 @@ static int vfio_irq_ctx_alloc_num(struct vfio_pci_core_device *vdev,
 	return ret;
 }
 
+static bool vfio_irq_ctx_range_allocated(struct vfio_pci_core_device *vdev,
+					 unsigned int start, unsigned int count)
+{
+	struct vfio_pci_irq_ctx *ctx;
+	unsigned int i;
+
+	for (i = start; i < start + count; i++) {
+		ctx = xa_load(&vdev->ctx, i);
+		if (!ctx)
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * INTx
  */
@@ -270,8 +285,6 @@ static int vfio_intx_enable(struct vfio_pci_core_device *vdev)
 		return -EINVAL;
 	}
 
-	vdev->num_ctx = 1;
-
 	/*
 	 * If the virtual interrupt is masked, restore it.  Devices
 	 * supporting DisINTx can be masked at the hardware level
@@ -358,7 +371,6 @@ static void vfio_intx_disable(struct vfio_pci_core_device *vdev)
 	}
 	vfio_intx_set_signal(vdev, -1);
 	vdev->irq_type = VFIO_PCI_NUM_IRQS;
-	vdev->num_ctx = 0;
 	vfio_irq_ctx_free_all(vdev);
 }
 
@@ -399,7 +411,6 @@ static int vfio_msi_enable(struct vfio_pci_core_device *vdev, int nvec, bool msi
 	}
 	vfio_pci_memory_unlock_and_restore(vdev, cmd);
 
-	vdev->num_ctx = nvec;
 	vdev->irq_type = msix ? VFIO_PCI_MSIX_IRQ_INDEX :
 				VFIO_PCI_MSI_IRQ_INDEX;
 
@@ -423,9 +434,6 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 	int irq, ret;
 	u16 cmd;
 
-	if (vector >= vdev->num_ctx)
-		return -EINVAL;
-
 	ctx = vfio_irq_ctx_get(vdev, vector);
 	if (!ctx)
 		return -EINVAL;
@@ -500,7 +508,7 @@ static int vfio_msi_set_block(struct vfio_pci_core_device *vdev, unsigned start,
 	int i, ret = 0;
 	unsigned int j;
 
-	if (start >= vdev->num_ctx || start + count > vdev->num_ctx)
+	if (!vfio_irq_ctx_range_allocated(vdev, start, count))
 		return -EINVAL;
 
 	for (i = 0, j = start; i < count && !ret; i++, j++) {
@@ -541,7 +549,6 @@ static void vfio_msi_disable(struct vfio_pci_core_device *vdev, bool msix)
 		pci_intx(pdev, 0);
 
 	vdev->irq_type = VFIO_PCI_NUM_IRQS;
-	vdev->num_ctx = 0;
 	vfio_irq_ctx_free_all(vdev);
 }
 
@@ -677,7 +684,10 @@ static int vfio_pci_set_msi_trigger(struct vfio_pci_core_device *vdev,
 		return ret;
 	}
 
-	if (!irq_is(vdev, index) || start + count > vdev->num_ctx)
+	if (!irq_is(vdev, index))
+		return -EINVAL;
+
+	if (!vfio_irq_ctx_range_allocated(vdev, start, count))
 		return -EINVAL;
 
 	for (i = start; i < start + count; i++) {
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 61d7873a3973..148fd1ae6c1c 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -60,7 +60,6 @@ struct vfio_pci_core_device {
 	spinlock_t		irqlock;
 	struct mutex		igate;
 	struct xarray		ctx;
-	int			num_ctx;
 	int			irq_type;
 	int			num_regions;
 	struct vfio_pci_region	*region;
-- 
2.34.1