[PATCH] Add interrupt remapping support

[Demi Marie Obenour <demiobenour@gmail.com>]

This adds interrupt remapping to the virtio-IOMMU device.  This is
needed to support deprivileged userspace drivers on x86_64 and other
platforms where interrupt remapping is the job of the IOMMU.  It is not
needed on AArch64 and must not be supported on that platform.
---
 device-types/iommu/description.tex | 70 +++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/device-types/iommu/description.tex b/device-types/iommu/description.tex
index f8cbe88..0a3bcab 100644
--- a/device-types/iommu/description.tex
+++ b/device-types/iommu/description.tex
@@ -3,7 +3,8 @@ \section{IOMMU device}\label{sec:Device Types / IOMMU Device}
 The virtio-iommu device manages Direct Memory Access (DMA) from one or
 more endpoints. It may act both as a proxy for physical IOMMUs managing
 devices assigned to the guest, and as virtual IOMMU managing emulated and
-paravirtualized devices.
+paravirtualized devices.  On some platforms, it is also responsible for
+interrupt remapping.
 
 The driver first discovers endpoints managed by the virtio-iommu device
 using platform specific mechanisms. It then sends requests to create
@@ -74,6 +75,13 @@ \subsection{Feature bits}\label{sec:Device Types / IOMMU Device / Feature bits}
   whether endpoints that are attached to a domain are in bypass
   mode.
 
+\item[VIRTIO_IOMMU_F_IRQ_MAP_UNMAP (7)]
+  Interrupt remapping is available. This is architecture specific
+  and MUST NOT be negotiated on architectures such as AArch64 where
+  interrupt remapping is not handled by the IOMMU.  If this feature
+  is negotiated, all interrupts from endpoints that are not in
+  bypass mode are initially disabled.
+
 \end{description}
 
 \drivernormative{\subsubsection}{Feature bits}{Device Types / IOMMU Device / Feature bits}
@@ -531,6 +539,66 @@ \subsubsection{MAP request}\label{sec:Device Types / IOMMU Device / Device opera
 range mapped with VIRTIO_IOMMU_MAP_F_WRITE but not
 VIRTIO_IOMMU_MAP_F_READ.
 
+\subsubsection{IRQ MAP request}\label{sec:Device Types / IOMMU Device / Device operations / IRQ MAP request}
+
+\begin{lstlisting}
+struct virtio_iommu_req_irq_map {
+  struct virtio_iommu_req_head head;
+  le32  domain;
+  le64  msi_address;
+  le32  msi_payload;
+  le32  vector_id;
+  le32  vcpu_id;
+  le32  flags;
+  u8    reserved[4];
+  struct virtio_iommu_req_tail tail;
+};
+\end{lstlisting}
+
+Map a host MSI to a guest MSI directed at the given vCPU.  vCPUs range from 0 to
+$2^{32} - 2$ inclusive.  $2^{32} - 1$ is reserved and means ``no vCPU'',
+effectively disabling the interrupt.  Any previous mapping of the MSI is overwritten.
+
+This request takes effect immediately.  It is the device's job to flush caches if
+necessary.  However, any interrupts that are pending remain pending.
+
+The set of permitted values for \field{msi_address} and \field{msi_payload}
+is architecture-dependent.  Invalid values include, but are not limited to:
+
+\begin{itemize}
+\item Values that are not in the architecture-dependent range of MSI addresses.
+\item Values that have bits set that are ignored by the physical IOMMU.
+\item Values that have reserved bits set.
+\item Values that would cause the MSI to not be subject to interrupt remapping,
+      and which the host must therefore block for its own security.
+\end{itemize}
+
+This request is only available when VIRTIO_IOMMU_F_IRQ_MAP_UNMAP has been negotiated.
+
+\drivernormative{\paragraph}{IRQ MAP request}{Device Types / IOMMU Device / Device operations / IRQ MAP request}
+
+The driver SHOULD set undefined \field{flags} bits to zero.
+
+The driver SHOULD NOT send IRQ MAP requests on a bypass domain.
+
+The driver SHOULD NOT choose values for \field{msi_address} or \field{msi_payload}
+that are invalid for the CPU architecture.
+
+The driver SHOULD NOT choose a \field{vcpu_id} that corresponds to a vCPU that does
+not exist and is not $2^{32} - 1$.
+
+\devicenormative{\paragraph}{IRQ MAP request}{Device Types / IOMMU Device / Device operations / IRQ MAP request}
+
+If \field{msi_address} or \field{msi_payload} is invalid for the CPU architecture,
+the device SHOULD reject the request and set \field{status} to VIRTIO_IOMMU_S_INVAL.
+
+If \field{domain} does not exist, the device SHOULD reject the request and
+set \field{status} to VIRTIO_IOMMU_S_NOENT.
+
+If \field{vcpu_id} does not correspond to a CPU that is running in the guest
+and is not $2^{32} - 1$, the device SHOULD reject the request and set
+\field{status} to VIRTIO_IOMMU_S_NOENT.
+
 \subsubsection{UNMAP request}\label{sec:Device Types / IOMMU Device / Device operations / UNMAP request}
 
 \begin{lstlisting}
-- 
Sincerely,
Demi Marie Obenour