[PATCH v2 1/1] virtio-pmem: Support describing pmem as shared memory region

[tstark@linux.microsoft.com]

From: Taylor Stark <tstark@microsoft.com>

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 <tstark@microsoft.com>
---
 conformance.tex |  1 +
 virtio-pmem.tex | 30 +++++++++++++++++++++++++-----
 2 files changed, 26 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..9f25664 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 +53,29 @@ \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}
+
+The driver SHOULD query the physical address ranges where the pmem was mapped.
+If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver SHOULD query
+shared memory ID 0 for the physical address ranges and MUST NOT use \field{start}
+or \field{size}. Else, the driver SHOULD read the physical address ranges from
+\field{start} and \field{size}.
+
 \drivernormative{\subsubsection}{Driver Initialization: Filesystem direct access}{Device Types / PMEM Driver / Driver Initialization / Direct access}
 
 Driver SHOULD enable filesystem direct access operations for
-- 
2.32.0