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Message-ID: <20230330164214.67ccbdfa.alex.williamson@redhat.com>
Date: Thu, 30 Mar 2023 16:42:14 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: jgg@...dia.com, yishaih@...dia.com,
shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
tglx@...utronix.de, darwi@...utronix.de, kvm@...r.kernel.org,
dave.jiang@...el.com, jing2.liu@...el.com, ashok.raj@...el.com,
fenghua.yu@...el.com, tom.zanussi@...ux.intel.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 7/8] vfio/pci: Support dynamic MSI-x
On Thu, 30 Mar 2023 16:40:50 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:
> On Tue, 28 Mar 2023 14:53:34 -0700
> Reinette Chatre <reinette.chatre@...el.com> 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 if supported by the device. Keep 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@...el.com>
> > ---
> > Changes since RFC V1:
> > - Add pointer to interrupt context as function parameter to
> > vfio_irq_ctx_free(). (Alex)
> > - Initialize new_ctx to false. (Dan Carpenter)
> > - Only support dynamic allocation if device supports it. (Alex)
> >
> > drivers/vfio/pci/vfio_pci_intrs.c | 93 +++++++++++++++++++++++++------
> > 1 file changed, 76 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> > index b3a258e58625..755b752ca17e 100644
> > --- a/drivers/vfio/pci/vfio_pci_intrs.c
> > +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> > @@ -55,6 +55,13 @@ 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,
> > + struct vfio_pci_irq_ctx *ctx, unsigned long index)
> > +{
> > + xa_erase(&vdev->ctx, index);
> > + kfree(ctx);
> > +}
Also, the function below should use this rather than open coding the
same now. Thanks,
Alex
> > +
> > static void vfio_irq_ctx_free_all(struct vfio_pci_core_device *vdev)
> > {
> > struct vfio_pci_irq_ctx *ctx;
> > @@ -409,33 +416,62 @@ 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 = {};
> > + bool allow_dyn_alloc = false;
> > struct eventfd_ctx *trigger;
> > + bool new_ctx = false;
> > int irq, ret;
> > u16 cmd;
> >
> > + /* Only MSI-X allows dynamic allocation. */
> > + if (msix && pci_msix_can_alloc_dyn(vdev->pdev))
> > + allow_dyn_alloc = true;
>
> Should vfio-pci-core probe this and store it in a field on
> vfio_pci_core_device so that we can simply use something like
> vdev->has_dyn_msix throughout?
>
> > +
> > ctx = vfio_irq_ctx_get(vdev, vector);
> > - if (!ctx)
> > + if (!ctx && !allow_dyn_alloc)
> > 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 (allow_dyn_alloc) {
>
> It almost seems easier to define msix_map in each scope that it's used:
>
> struct msi_map map = { .index = vector,
> .virq = irq };
>
> > + 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 (allow_dyn_alloc) {
> > + vfio_irq_ctx_free(vdev, ctx, vector);
> > + ctx = NULL;
> > + }
> > }
> >
> > if (fd < 0)
> > return 0;
> >
> > + if (!ctx) {
> > + ctx = vfio_irq_ctx_alloc_single(vdev, vector);
> > + if (!ctx)
> > + return -ENOMEM;
> > + 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)) {
> > @@ -443,25 +479,38 @@ 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);
>
> struct msi_map map = pci_msix_alloc_irq_at(pdev,
> vector, NULL);
> > + 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.
> > + */
>
> You've only just copied this comment down to here, but I think it's a
> bit stale. Maybe we should update it to something that helps explain
> this split better, maybe:
>
> /*
> * If the vector was previously allocated, refresh the
> * on-device message data before enabling in case it had
> * been cleared or corrupted since writing.
> */
>
> IIRC, that was the purpose of writing it back to the device and the
> blocking of direct access is no longer accurate anyway.
>
> > + struct msi_msg msg;
> > +
> > + get_cached_msi_msg(irq, &msg);
> > + pci_write_msi_msg(irq, &msg);
> > + }
> > }
> >
> > 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;
> > @@ -477,11 +526,21 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
> >
> > return 0;
> >
> > +out_free_irq_locked:
> > + if (allow_dyn_alloc && new_ctx) {
>
> struct msi_map map = { .index = vector,
> .virq = irq };
>
> > + 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 (allow_dyn_alloc && new_ctx)
> > + vfio_irq_ctx_free(vdev, ctx, vector);
> > return ret;
> > }
> >
>
> Do we really need the new_ctx test in the above cases? Thanks,
>
> Alex
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