On Thu, Feb 04, 2021 at 12:09:06PM -0700, Jon Derrick wrote:
> VMD will retransmit child device MSI/X using its own MSI/X table and
> requester-id. This limits the number of MSI/X available to the whole
> child device domain to the number of VMD MSI/X interrupts.
>
> Some VMD devices have a mode where this remapping can be disabled,
> allowing child device interrupts to bypass processing with the VMD MSI/X
> domain interrupt handler and going straight the child device interrupt
> handler, allowing for better performance and scaling. The requester-id
> still gets changed to the VMD endpoint's requester-id, and the interrupt
> remapping handlers have been updated to properly set IRTE for child
> device interrupts to the VMD endpoint's context.
>
> Some VMD platforms have existing production BIOS which rely on MSI/X
> remapping and won't explicitly program the MSI/X remapping bit. This
> re-enables MSI/X remapping on unload.
Trivial comments below. Would you mind using "MSI-X" instead of
"MSI/X" so it matches the usage in the PCIe specs? Several mentions
above (including subject) and below.
> Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> ---
> drivers/pci/controller/vmd.c | 60 ++++++++++++++++++++++++++++--------
> 1 file changed, 48 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 5e80f28f0119..a319ce49645b 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -59,6 +59,13 @@ enum vmd_features {
> * be used for MSI remapping
> */
> VMD_FEAT_OFFSET_FIRST_VECTOR = (1 << 3),
> +
> + /*
> + * Device can bypass remapping MSI/X transactions into its MSI/X table,
> + * avoding the requirement of a VMD MSI domain for child device
s/avoding/avoiding/
> + * interrupt handling
Maybe a period at the end of the sentence.
> + */
> + VMD_FEAT_BYPASS_MSI_REMAP = (1 << 4),
> };
>
> /*
> @@ -306,6 +313,15 @@ static struct msi_domain_info vmd_msi_domain_info = {
> .chip = &vmd_msi_controller,
> };
>
> +static void vmd_enable_msi_remapping(struct vmd_dev *vmd, bool enable)
> +{
> + u16 reg;
> +
> + pci_read_config_word(vmd->dev, PCI_REG_VMCONFIG, ®);
> + reg = enable ? (reg & ~0x2) : (reg | 0x2);
Would be nice to have a #define for 0x2.
> + pci_write_config_word(vmd->dev, PCI_REG_VMCONFIG, reg);
> +}
> +
> static int vmd_create_irq_domain(struct vmd_dev *vmd)
> {
> struct fwnode_handle *fn;
> @@ -325,6 +341,13 @@ static int vmd_create_irq_domain(struct vmd_dev *vmd)
>
> static void vmd_remove_irq_domain(struct vmd_dev *vmd)
> {
> + /*
> + * Some production BIOS won't enable remapping between soft reboots.
> + * Ensure remapping is restored before unloading the driver.
> + */
> + if (!vmd->msix_count)
> + vmd_enable_msi_remapping(vmd, true);
> +
> if (vmd->irq_domain) {
> struct fwnode_handle *fn = vmd->irq_domain->fwnode;
>
> @@ -679,15 +702,31 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>
> sd->node = pcibus_to_node(vmd->dev->bus);
>
> - ret = vmd_create_irq_domain(vmd);
> - if (ret)
> - return ret;
> -
> /*
> - * Override the irq domain bus token so the domain can be distinguished
> - * from a regular PCI/MSI domain.
> + * Currently MSI remapping must be enabled in guest passthrough mode
> + * due to some missing interrupt remapping plumbing. This is probably
> + * acceptable because the guest is usually CPU-limited and MSI
> + * remapping doesn't become a performance bottleneck.
> */
> - irq_domain_update_bus_token(vmd->irq_domain, DOMAIN_BUS_VMD_MSI);
> + if (!(features & VMD_FEAT_BYPASS_MSI_REMAP) || offset[0] || offset[1]) {
> + ret = vmd_alloc_irqs(vmd);
> + if (ret)
> + return ret;
> +
> + vmd_enable_msi_remapping(vmd, true);
> +
> + ret = vmd_create_irq_domain(vmd);
> + if (ret)
> + return ret;
> +
> + /*
> + * Override the irq domain bus token so the domain can be
> + * distinguished from a regular PCI/MSI domain.
> + */
> + irq_domain_update_bus_token(vmd->irq_domain, DOMAIN_BUS_VMD_MSI);
> + } else {
> + vmd_enable_msi_remapping(vmd, false);
> + }
>
> pci_add_resource(&resources, &vmd->resources[0]);
> pci_add_resource_offset(&resources, &vmd->resources[1], offset[0]);
> @@ -753,10 +792,6 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id)
> if (features & VMD_FEAT_OFFSET_FIRST_VECTOR)
> vmd->first_vec = 1;
>
> - err = vmd_alloc_irqs(vmd);
> - if (err)
> - return err;
> -
> spin_lock_init(&vmd->cfg_lock);
> pci_set_drvdata(dev, vmd);
> err = vmd_enable_domain(vmd, features);
> @@ -825,7 +860,8 @@ static const struct pci_device_id vmd_ids[] = {
> .driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP,},
> {PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_VMD_28C0),
> .driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW |
> - VMD_FEAT_HAS_BUS_RESTRICTIONS,},
> + VMD_FEAT_HAS_BUS_RESTRICTIONS |
> + VMD_FEAT_BYPASS_MSI_REMAP,},
> {PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x467f),
> .driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
> VMD_FEAT_HAS_BUS_RESTRICTIONS |
> --
> 2.27.0
>
