[PATCH v3 1/3] shared-mem: introduce page alignment restrictions

[Sergio Lopez <slp@redhat.com>]

Add a subsection for page alignment restrictions and introduce the
VIRTIO_F_SHM_PAGE_SIZE feature bit.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 content.tex    | 10 ++++++++--
 shared-mem.tex |  7 +++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/content.tex b/content.tex
index c17ffa6..c8826a2 100644
--- a/content.tex
+++ b/content.tex
@@ -99,10 +99,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B
 \begin{description}
 \item[0 to 23, and 50 to 127] Feature bits for the specific device type
 
-\item[24 to 41] Feature bits reserved for extensions to the queue and
+\item[24 to 42] Feature bits reserved for extensions to the queue and
   feature negotiation mechanisms, see \ref{sec:Reserved Feature Bits}
 
-\item[42 to 49, and 128 and above] Feature bits reserved for future extensions.
+\item[43 to 49, and 128 and above] Feature bits reserved for future extensions.
 \end{description}
 
 \begin{note}
@@ -872,6 +872,12 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 	\ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
 	handling features reserved for future use.
 
+  \item[VIRTIO_F_SHM_PAGE_SIZE(42)] This feature indicates that the device
+  transport provides information about the supported page size and expects the
+  driver to honor the alignment restrictions derived from it when requesting
+  mappings on the corresponding shared memory region.
+  See also \ref {sec:Basic Facilities of a Virtio Device / Shared Memory Regions / Page alignment restrictions}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
diff --git a/shared-mem.tex b/shared-mem.tex
index 6e6f6c4..dd90cb7 100644
--- a/shared-mem.tex
+++ b/shared-mem.tex
@@ -34,6 +34,13 @@ \subsection{Addressing within regions}\label{sec:Basic Facilities of a Virtio De
 The \field{shmid} may be explicit or may be inferred from the
 context of the reference.
 
+\subsection{Page alignment restrictions}\label{sec:Basic Facilities of a Virtio Device / Shared Memory Regions / Page alignment restrictions}
+
+If VIRTIO_F_SHM_PAGE_SIZE has been negotiated, when requesting
+the device to map memory into a shared memory region, the driver
+MUST obtain the page size information from the transport and honor
+the page alignment constrains derived from that page size.
+
 \devicenormative{\subsection}{Shared Memory Regions}{Basic Facilities of a Virtio
 Device / Shared Memory Regions}
 Shared memory regions MUST NOT expose shared memory regions which
-- 
2.49.0