On Wed, 15 Mar 2023 13:59:27 -0700
Reinette Chatre <reinette.chatre@xxxxxxxxx> wrote:
> Recently introduced pci_msix_alloc_irq_at() and pci_msix_free_irq()
> enables an individual MSI-X index to be allocated and freed after
> MSI-X enabling.
>
> Support dynamic MSI-X by keeping the association between allocated
> interrupt and vfio interrupt context. Allocate new context together
> with the new interrupt if no interrupt context exist for an MSI-X
> interrupt. Similarly, release an interrupt with its context.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> ---
>
> Guidance is appreciated on expectations regarding maintaining
> existing error behavior. Earlier patch introduced the
> vfio_irq_ctx_range_allocated() helper to maintain existing error
> behavior. Now, this helper needs to be disabled for MSI-X. User
> space not wanting to dynamically allocate MSI-X interrupts, but
> providing invalid range when providing a new ACTION will now
> obtain new interrupts or new failures (potentially including freeing
> of existing interrupts) if the allocation of the new interrupts fail.
>
> drivers/vfio/pci/vfio_pci_intrs.c | 101 ++++++++++++++++++++++++------
> 1 file changed, 83 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index b375a12885ba..954a70575802 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -55,6 +55,18 @@ struct vfio_pci_irq_ctx *vfio_irq_ctx_get(struct vfio_pci_core_device *vdev,
> return xa_load(&vdev->ctx, index);
> }
>
> +static void vfio_irq_ctx_free(struct vfio_pci_core_device *vdev,
> + unsigned long index)
> +{
> + struct vfio_pci_irq_ctx *ctx;
> +
> + ctx = xa_load(&vdev->ctx, index);
> + if (ctx) {
> + xa_erase(&vdev->ctx, index);
> + kfree(ctx);
> + }
> +}
The only places calling this have a known valid ctx, so it seems
redundant that we xa_load it again. Should ctx be a function arg to
reduce this to simply xa_erase() + kfree()?
> +
> static void vfio_irq_ctx_free_all(struct vfio_pci_core_device *vdev)
> {
> struct vfio_pci_irq_ctx *ctx;
> @@ -430,33 +442,63 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
> {
> struct pci_dev *pdev = vdev->pdev;
> struct vfio_pci_irq_ctx *ctx;
> + struct msi_map msix_map = {};
> struct eventfd_ctx *trigger;
> + bool new_ctx;
> int irq, ret;
> u16 cmd;
>
> ctx = vfio_irq_ctx_get(vdev, vector);
> - if (!ctx)
> + /* Only MSI-X allows dynamic allocation. */
> + if (!msix && !ctx)
> return -EINVAL;
> +
> irq = pci_irq_vector(pdev, vector);
> + /* Context and interrupt are always allocated together. */
> + WARN_ON((ctx && irq == -EINVAL) || (!ctx && irq != -EINVAL));
>
> - if (ctx->trigger) {
> + if (ctx && ctx->trigger) {
> irq_bypass_unregister_producer(&ctx->producer);
>
> cmd = vfio_pci_memory_lock_and_enable(vdev);
> free_irq(irq, ctx->trigger);
> + if (msix) {
> + msix_map.index = vector;
> + msix_map.virq = irq;
> + pci_msix_free_irq(pdev, msix_map);
> + irq = -EINVAL;
> + }
> vfio_pci_memory_unlock_and_restore(vdev, cmd);
> kfree(ctx->name);
> eventfd_ctx_put(ctx->trigger);
> ctx->trigger = NULL;
> + if (msix) {
> + vfio_irq_ctx_free(vdev, vector);
> + ctx = NULL;
> + }
> }
>
> if (fd < 0)
> return 0;
>
> + if (!ctx) {
> + ret = vfio_irq_ctx_alloc_single(vdev, vector);
> + if (ret)
> + return ret;
> + ctx = vfio_irq_ctx_get(vdev, vector);
This suggests vfio_irq_ctx_alloc_single() should return ctx.
> + if (!ctx) {
> + ret = -EINVAL;
> + goto out_free_ctx;
> + }
> + new_ctx = true;
> + }
> +
> ctx->name = kasprintf(GFP_KERNEL_ACCOUNT, "vfio-msi%s[%d](%s)",
> msix ? "x" : "", vector, pci_name(pdev));
> - if (!ctx->name)
> - return -ENOMEM;
> + if (!ctx->name) {
> + ret = -ENOMEM;
> + goto out_free_ctx;
> + }
>
> trigger = eventfd_ctx_fdget(fd);
> if (IS_ERR(trigger)) {
> @@ -464,25 +506,38 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
> goto out_free_name;
> }
>
> - /*
> - * The MSIx vector table resides in device memory which may be cleared
> - * via backdoor resets. We don't allow direct access to the vector
> - * table so even if a userspace driver attempts to save/restore around
> - * such a reset it would be unsuccessful. To avoid this, restore the
> - * cached value of the message prior to enabling.
> - */
> cmd = vfio_pci_memory_lock_and_enable(vdev);
> if (msix) {
> - struct msi_msg msg;
> -
> - get_cached_msi_msg(irq, &msg);
> - pci_write_msi_msg(irq, &msg);
> + if (irq == -EINVAL) {
> + msix_map = pci_msix_alloc_irq_at(pdev, vector, NULL);
It looks to me like we need to support MSI-X with both NORESIZE
behavior and dynamic allocation based on pci_msix_can_alloc_dyn().
It's not entirely clear to me where this is and isn't supported, but
the existence of the test helper suggests we can't assume support.
> + if (msix_map.index < 0) {
> + vfio_pci_memory_unlock_and_restore(vdev, cmd);
> + ret = msix_map.index;
> + goto out_put_eventfd_ctx;
> + }
> + irq = msix_map.virq;
> + } else {
> + /*
> + * The MSIx vector table resides in device memory which
> + * may be cleared via backdoor resets. We don't allow
> + * direct access to the vector table so even if a
> + * userspace driver attempts to save/restore around
> + * such a reset it would be unsuccessful. To avoid
> + * this, restore the cached value of the message prior
> + * to enabling.
> + */
> + struct msi_msg msg;
> +
> + get_cached_msi_msg(irq, &msg);
> + pci_write_msi_msg(irq, &msg);
> + }
I don't follow when this latter branch is ever taken in the new flow.
It's stated earlier that ctx and irq are coupled, and I believe so is
trigger. So if we had a previous ctx and irq (and trigger), we removed
it and irq is now always -EINVAL here. Thanks,
Alex
> }
>
> ret = request_irq(irq, vfio_msihandler, 0, ctx->name, trigger);
> - vfio_pci_memory_unlock_and_restore(vdev, cmd);
> if (ret)
> - goto out_put_eventfd_ctx;
> + goto out_free_irq_locked;
> +
> + vfio_pci_memory_unlock_and_restore(vdev, cmd);
>
> ctx->producer.token = trigger;
> ctx->producer.irq = irq;
> @@ -498,11 +553,21 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
>
> return 0;
>
> +out_free_irq_locked:
> + if (msix && new_ctx) {
> + msix_map.index = vector;
> + msix_map.virq = irq;
> + pci_msix_free_irq(pdev, msix_map);
> + }
> + vfio_pci_memory_unlock_and_restore(vdev, cmd);
> out_put_eventfd_ctx:
> eventfd_ctx_put(trigger);
> out_free_name:
> kfree(ctx->name);
> ctx->name = NULL;
> +out_free_ctx:
> + if (msix && new_ctx)
> + vfio_irq_ctx_free(vdev, vector);
> return ret;
> }
>
> @@ -512,7 +577,7 @@ static int vfio_msi_set_block(struct vfio_pci_core_device *vdev, unsigned start,
> int i, ret = 0;
> unsigned int j;
>
> - if (!vfio_irq_ctx_range_allocated(vdev, start, count))
> + if (!msix && !vfio_irq_ctx_range_allocated(vdev, start, count))
> return -EINVAL;
>
> for (i = 0, j = start; i < count && !ret; i++, j++) {
