From: Taylor Stark <>
Update the virtio-pmem RFC spec to add support for describing the pmem region
as a shared memory window. This is required to support virtio-pmem in Hyper-V,
since Hyper-V only allows PCI devices to operate on memory ranges defined via
BARs. When using the virtio PCI transport, shared memory regions are described
via PCI BARs.
Signed-off-by: Taylor Stark <>
---
conformance.tex | 1 +
virtio-pmem.tex | 34 +++++++++++++++++++++++++++++-----
2 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/conformance.tex b/conformance.tex
index 33fdac9..8e414eb 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -201,6 +201,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
\begin{itemize}
\item \ref{devicenormative:Device Types / PMEM Device / Device Initialization}
+\item \ref{drivernormative:Device Types / PMEM Driver / Driver Initialization}
\item \ref{drivernormative:Device Types / PMEM Driver / Driver Initialization / Direct access}
\item \ref{drivernormative:Device Types / PMEM Driver / Driver Initialization / Virtio flush}
\item \ref{drivernormative:Device Types / PMEM Driver / Driver Operation / Virtqueue command}
diff --git a/virtio-pmem.tex b/virtio-pmem.tex
index 04e07bb..ceb62db 100644
--- a/virtio-pmem.tex
+++ b/virtio-pmem.tex
@@ -19,7 +19,10 @@ \subsection{Virtqueues}\label{sec:Device Types / PMEM Device / Virtqueues}
\subsection{Feature bits}\label{sec:Device Types / PMEM Device / Feature bits}
-There are currently no feature bits defined for this device.
+\begin{description}
+\item[VIRTIO_PMEM_F_SHMEM_REGION (0)] The guest physical address range will be
+indicated as a shared memory region.
+\end{description}
\subsection{Device configuration layout}\label{sec:Device Types / PMEM Device / Device configuration layout}
@@ -38,11 +41,11 @@ \subsection{Device configuration layout}\label{sec:Device Types / PMEM Device /
\subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device Initialization}
Device hotplugs physical memory to guest address space. Persistent memory device
-is emulated with file backed memory at host side.
-
+is emulated with file backed memory at host side. The device indicates the guest
+physical address to the driver in one of two ways:
\begin{enumerate}
-\item Guest vpmem start is read from \field{start}.
-\item Guest vpmem end is read from \field{size}.
+\item As a guest absolute address.
+\item As a shared memory region.
\end{enumerate}
\devicenormative{\subsubsection}{Device Initialization}{Device Types / PMEM Device / Device Initialization}
@@ -50,12 +53,33 @@ \subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device
File backed memory SHOULD be memory mapped to guest address space with SHARED
memory mapping.
+If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the device MUST indicate the
+guest physical address as a shared memory region. The device MUST use shared
+memory region ID 0. The device SHOULD set \field{start} and \field{size} to zero.
+
+If VIRTIO_PMEM_F_SHMEM_REGION has not been negotiated, the device MUST indicate
+the guest physical address as a guest absolute address. The device MUST set
+\field{start} to the absolute address and \field{size} to the size of the
+address range, in bytes.
+
\subsection{Driver Initialization}\label{sec:Device Types / PMEM Driver / Driver Initialization}
Driver hotplugs the physical memory and registers associated
region with the pmem API. Also, configures a flush callback
function with the corresponding region.
+\drivernormative{\subsubsection}{Driver Initialization}{Device Types / PMEM Driver / Driver Initialization}
+
+In order to discover the physical address ranges where the pmem was
+mapped:
+
+If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver MUST query
+shared memory ID 0 for the physical address ranges, and MUST NOT use
+\field{start} or \field{stop}.
+
+If VIRTIO_PMEM_F_SHMEM_REGION has not been negotiated, the driver MUST
+read the physical address ranges from \field{start} and \field{stop}.
+
\drivernormative{\subsubsection}{Driver Initialization: Filesystem direct access}{Device Types / PMEM Driver / Driver Initialization / Direct access}
Driver SHOULD enable filesystem direct access operations for
--
2.31.0.vfs.0.1
