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Subject: [PATCH v2 5/5] virtio-mem: describe interaction with memory properties
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 | 61 +++++++++++++++++++++++++++++++++----------------- 1 file changed, 40 insertions(+), 21 deletions(-) diff --git a/virtio-mem.tex b/virtio-mem.tex index dce035c..0a6d558 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 comparable RAM in the same configuration. + \subsection{Device ID}\label{sec:Device Types / Memory Device / Device ID} 24 @@ -47,7 +57,9 @@ \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 is not allowed to -access unplugged memory. +access unplugged memory. \footnote{On platforms with memory properties that +might get modified implicitly on memory access, this feature is expected to +be offered by the device.} \end{description} \subsection{Device configuration layout}\label{sec:Device Types / Memory Device / Device configuration layout} @@ -159,8 +171,8 @@ \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 +235,24 @@ \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 memory of unplugged memory blocks. +The driver MUST NOT write memory or modify memory properties of +unplugged memory blocks. -The driver MUST NOT read memory of 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}. -The driver MUST NOT read memory of unplugged memory blocks inside -\field{usable_region_size} via DMA. +The driver MUST NOT read memory or query memory properties of unplugged memory +blocks inside \field{usable_region_size} via DMA. If VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE has not been negotiated, the driver -SHOULD NOT read memory of unplugged memory blocks inside -\field{usable_region_size} via the CPU. +SHOULD NOT read memory or query memory properties of unplugged memory blocks +inside \field{usable_region_size} via the CPU. If VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE has been negotiated, the driver -MUST NOT read memory of unplugged memory blocks. +MUST NOT read memory or query memory properties of unplugged memory blocks. -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. @@ -257,18 +270,24 @@ \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 +comparable RAM. -The device MUST NOT change the content of plugged memory blocks. +The device MAY modify memory of unplugged memory blocks or reset memory +properties of such memory blocks to platform defaults at any time. -The device MUST allow the driver to read and write memory of plugged -memory blocks. +The device MUST NOT modify memory or memory properties of plugged memory +blocks. + +The device MUST allow the driver to read and write memory and to query +and modify memory attributes of plugged memory blocks. If VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE has not been negotiated, the device -MUST allow the driver to read memory of unplugged memory blocks inside -\field{usable_region_size} via the CPU. \footnote{To allow for simplified -dumping of memory. The CPU is expected to copy such memory to another -location before starting DMA.} +MUST allow the driver to read memory and to query memory properties of +unplugged memory blocks inside \field{usable_region_size} via the CPU. +\footnote{To allow for simplified dumping of memory. The CPU is expected to +copy such memory to another location before starting DMA.} The device MAY change the state of memory blocks during system resets. -- 2.31.1
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