The Intel Volume Management Device acts similar to a PCI-to-PCI bridge in that it changes downstream devices' requester-ids to its own. As VMD supports PCIe devices, it has its own MSI-X table and transmits child device MSI-X by remapping child device MSI-X and handling like a demultiplexer. Some newer VMD devices (Icelake Server) have an option to bypass the VMD MSI-X remapping table. This allows for better performance scaling as the child device MSI-X won't be limited by VMD's MSI-X count and IRQ handler. V2->V3: Trivial comment fixes Added acks V1->V2: Updated for 5.12-next Moved IRQ allocation and remapping enable/disable to a more logical location V1 patches 1-4 were already merged V1, 5/6: https://patchwork.kernel.org/project/linux-pci/patch/20200728194945.14126-6-jonathan.derrick@xxxxxxxxx/ V1, 6/6: https://patchwork.kernel.org/project/linux-pci/patch/20200728194945.14126-7-jonathan.derrick@xxxxxxxxx/ Jon Derrick (2): iommu/vt-d: Use Real PCI DMA device for IRTE PCI: vmd: Disable MSI-X remapping when possible drivers/iommu/intel/irq_remapping.c | 3 +- drivers/pci/controller/vmd.c | 61 +++++++++++++++++++++++------ 2 files changed, 51 insertions(+), 13 deletions(-) -- 2.27.0
