[virtio-comment] [PATCH v1 2/2] virtio-mem: describe interaction with memory properties

[David Hildenbrand <david@redhat.com>]

Let's describe how we expect the interaction with memory properties that
might be available on a specific platform for ordinary system RAM.

This is primarily a preparation for s390x support, which provides
storage keys and may provide storage attributes, depending on the system
configuration.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 virtio-mem.tex | 71 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 49 insertions(+), 22 deletions(-)

diff --git a/virtio-mem.tex b/virtio-mem.tex
index c4dd0d0..a1057cd 100644
--- a/virtio-mem.tex
+++ b/virtio-mem.tex
@@ -32,6 +32,16 @@ \section{Memory Device}\label{sec:Device Types / Memory Device}
 expose plugged memory blocks to the operating system as system RAM,
 available for the page allocator.
 
+Some platforms provide memory properties for system RAM that are usually
+queried and modified using special CPU instructions. Memory properties might
+be implicitly queried or modified on memory access. Memory properties can
+include advanced memory protection, access and change indication, or memory
+usage indication relevant in virtualized environments. \footnote{For example,
+s390x provides storage keys for each 4 KiB page and may, depending on the
+configuration, provide storage attributes for each 4 KiB page.} The device
+provides the exact same properties with the exact same semantics for
+plugged device memory as available for ordinary RAM in the same configuration.
+
 \subsection{Device ID}\label{sec:Device Types / Memory Device / Device ID}
 24
 
@@ -47,7 +57,8 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Device / Feature bits}
 \item[VIRTIO_MEM_F_ACPI_PXM (0)] The field \field{node_id} in the device
 configuration is valid and corresponds to an ACPI PXM.
 \item[VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE (1)] The driver MUST NOT access
-unplugged memory.
+unplugged memory. \footnote{This feature is expected to be enabled on platforms
+with memory properties that might get modified implicitly on memory access.}
 \end{description}
 
 \subsection{Device configuration layout}\label{sec:Device Types / Memory Device / Device configuration layout}
@@ -159,8 +170,8 @@ \subsection{Device Initialization}\label{Device Types / Memory Device / Device I
 
 The device MUST NOT change the state of memory blocks during device reset.
 
-The device MUST NOT change the content of plugged memory blocks during
-device reset.
+The device MUST NOT modify memory or memory properties of plugged memory
+blocks during device reset.
 
 \subsection{Device Operation}\label{sec:Device Types / Memory Device / Device Operation}
 
@@ -223,23 +234,30 @@ \subsection{Device Operation}\label{sec:Device Types / Memory Device / Device Op
 
 \drivernormative{\subsubsection}{Device Operation}{Device Types / Memory Device / Device Operation}
 
-The driver MUST NOT write to unplugged memory blocks.
+The driver MUST NOT write memory or modify memory properties of
+unplugged memory blocks.
 
-The driver MUST NOT read from unplugged memory blocks outside
-\field{usable_region_size}.
+The driver MUST NOT read memory or query memory properties of unplugged
+memory blocks outside \field{usable_region_size}.
 
 Without VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, the driver SHOULD NOT read
-memory of unplugged memory blocks inside \field{usable_region_size}.
+memory or query memory properties of unplugged memory blocks inside
+\field{usable_region_size}.
 
-With VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, the driver MUST NOT read memory of
-unplugged memory blocks.
+With VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, the driver MUST NOT read memory
+or query memory properties of unplugged memory blocks inside
+\field{usable_region_size}.
 
-The driver MUST NOT request to unplug memory blocks while the memory is
-still in use.
+The driver MUST NOT request unplug of memory blocks while corresponding memory
+or memory properties are still in use.
 
 The driver SHOULD initialize memory blocks after plugging them, the content
 is undefined.
 
+The driver SHOULD initialize memory properties of memory blocks after plugging
+them if it cannot deal with either the default settings or the previous
+setting.
+
 The driver SHOULD react to resize requests from the device
 (\field{requested_size} in the device configuration changed) by
 (un)plugging memory blocks.
@@ -253,25 +271,34 @@ \subsection{Device Operation}\label{sec:Device Types / Memory Device / Device Op
 
 \devicenormative{\subsubsection}{Device Operation}{Device Types / Memory Device / Device Operation}
 
-The device MAY change the content of unplugged memory blocks at any time.
+The device MUST provide the exact same memory properties with the exact same
+semantics for device memory the platform provides in the same configuration for
+ordinary RAM.
+
+The device MAY modify memory or reset memory properties to defaults of unplugged
+memory blocks at any time.
 
-The device MUST NOT change the content of plugged memory blocks.
+The device MUST NOT modify memory or memory properties of plugged memory
+blocks.
 
 Without VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, the device MUST allow the CPU to
-read memory of unplugged memory blocks inside \field{usable_region_size}.
-\footnote{To allow for simplified dumping of memory. The CPU is expected to
-copy such memory to another location before starting DMA.}
+read memory or query memory properties of unplugged memory blocks inside
+\field{usable_region_size}. \footnote{To allow for simplified dumping of
+memory. The CPU is expected to copy such memory to another location before
+starting DMA.}
 
 With VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, the device MAY allow the CPU to
-read memory of unplugged memory blocks inside \field{usable_region_size}.
+read memory or query memory properties of unplugged memory blocks inside
+\field{usable_region_size}.
 
-The device MAY allow to read from unplugged memory blocks inside the
-usable device-managed region via DMA.
+The device MAY allow to read memory or query memory properties of unplugged
+memory blocks inside \field{usable_region_size} via DMA.
 
-The device MAY allow to read from unplugged memory blocks outside
-the usable device-managed region.
+The device MAY allow to read memory or query memory properties of unplugged
+memory blocks outside \field{usable_region_size} via DMA.
 
-The device MAY allow to write to unplugged memory blocks.
+The device MAY allow to write memory or modify memory properties of unplugged
+memory blocks.
 
 The device MAY change the state of memory blocks during system resets.
 
-- 
2.31.1


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