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Subject: [PATCH v1 2/2] 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 | 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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