Merge tag 'x86-irq-2024-05-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 interrupt handling updates from Thomas Gleixner:
 "Add support for posted interrupts on bare metal.

  Posted interrupts is a virtualization feature which allows to inject
  interrupts directly into a guest without host interaction. The VT-d
  interrupt remapping hardware sets the bit which corresponds to the
  interrupt vector in a vector bitmap which is either used to inject the
  interrupt directly into the guest via a virtualized APIC or in case
  that the guest is scheduled out provides a host side notification
  interrupt which informs the host that an interrupt has been marked
  pending in the bitmap.

  This can be utilized on bare metal for scenarios where multiple
  devices, e.g. NVME storage, raise interrupts with a high frequency. In
  the default mode these interrupts are handles independently and
  therefore require a full roundtrip of interrupt entry/exit.

  Utilizing posted interrupts this roundtrip overhead can be avoided by
  coalescing these interrupt entries to a single entry for the posted
  interrupt notification. The notification interrupt then demultiplexes
  the pending bits in a memory based bitmap and invokes the
  corresponding device specific handlers.

  Depending on the usage scenario and device utilization throughput
  improvements between 10% and 130% have been measured.

  As this is only relevant for high end servers with multiple device
  queues per CPU attached and counterproductive for situations where
  interrupts are arriving at distinct times, the functionality is opt-in
  via a kernel command line parameter"

* tag 'x86-irq-2024-05-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/irq: Use existing helper for pending vector check
  iommu/vt-d: Enable posted mode for device MSIs
  iommu/vt-d: Make posted MSI an opt-in command line option
  x86/irq: Extend checks for pending vectors to posted interrupts
  x86/irq: Factor out common code for checking pending interrupts
  x86/irq: Install posted MSI notification handler
  x86/irq: Factor out handler invocation from common_interrupt()
  x86/irq: Set up per host CPU posted interrupt descriptors
  x86/irq: Reserve a per CPU IDT vector for posted MSIs
  x86/irq: Add a Kconfig option for posted MSI
  x86/irq: Remove bitfields in posted interrupt descriptor
  x86/irq: Unionize PID.PIR for 64bit access w/o casting
  KVM: VMX: Move posted interrupt descriptor out of VMX code

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 07e8817278a4..9d16fee6bdb8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -466,6 +466,17 @@ config X86_X2APIC
 
 	  If you don't know what to do here, say N.
 
+config X86_POSTED_MSI
+	bool "Enable MSI and MSI-x delivery by posted interrupts"
+	depends on X86_64 && IRQ_REMAP
+	help
+	  This enables MSIs that are under interrupt remapping to be delivered as
+	  posted interrupts to the host kernel. Interrupt throughput can
+	  potentially be improved by coalescing CPU notifications during high
+	  frequency bursts.
+
+	  If you don't know what to do here, say N.
+
 config X86_MPPARSE
 	bool "Enable MPS table" if ACPI
 	default y