KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 110 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/vimc.rst b/Documentation/admin-guide/media/vimc.rst
new file mode 100644
index 000000000..29d843a8d
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+++ b/Documentation/admin-guide/media/vimc.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+The Virtual Media Controller Driver (vimc)
+==========================================
+
+The vimc driver emulates complex video hardware using the V4L2 API and the Media
+API. It has a capture device and three subdevices: sensor, debayer and scaler.
+
+Topology
+--------
+
+The topology is hardcoded, although you could modify it in vimc-core and
+recompile the driver to achieve your own topology. This is the default topology:
+
+.. _vimc_topology_graph:
+
+.. kernel-figure:: vimc.dot
+    :alt:   Diagram of the default media pipeline topology
+    :align: center
+
+    Media pipeline graph on vimc
+
+Configuring the topology
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each subdevice will come with its default configuration (pixelformat, height,
+width, ...). One needs to configure the topology in order to match the
+configuration on each linked subdevice to stream frames through the pipeline.
+If the configuration doesn't match, the stream will fail. The ``v4l-utils``
+package is a bundle of user-space applications, that comes with ``media-ctl`` and
+``v4l2-ctl`` that can be used to configure the vimc configuration. This sequence
+of commands fits for the default topology:
+
+.. code-block:: bash
+
+        media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
+        media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
+        media-ctl -d platform:vimc -V '"Scaler":0[fmt:RGB888_1X24/640x480]'
+        media-ctl -d platform:vimc -V '"Scaler":0[crop:(100,50)/400x150]'
+        media-ctl -d platform:vimc -V '"Scaler":1[fmt:RGB888_1X24/300x700]'
+        v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=300,height=700
+        v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
+
+Subdevices
+----------
+
+Subdevices define the behavior of an entity in the topology. Depending on the
+subdevice, the entity can have multiple pads of type source or sink.
+
+vimc-sensor:
+	Generates images in several formats using video test pattern generator.
+	Exposes:
+
+	* 1 Pad source
+
+vimc-lens:
+	Ancillary lens for a sensor. Supports auto focus control. Linked to
+	a vimc-sensor using an ancillary link. The lens supports FOCUS_ABSOLUTE
+	control.
+
+.. code-block:: bash
+
+	media-ctl -p
+	...
+	- entity 28: Lens A (0 pad, 0 link)
+			type V4L2 subdev subtype Lens flags 0
+			device node name /dev/v4l-subdev6
+	- entity 29: Lens B (0 pad, 0 link)
+			type V4L2 subdev subtype Lens flags 0
+			device node name /dev/v4l-subdev7
+	v4l2-ctl -d /dev/v4l-subdev7 -C focus_absolute
+	focus_absolute: 0
+
+
+vimc-debayer:
+	Transforms images in bayer format into a non-bayer format.
+	Exposes:
+
+	* 1 Pad sink
+	* 1 Pad source
+
+vimc-scaler:
+	Re-size the image to meet the source pad resolution. E.g.: if the sync
+	pad is configured to 360x480 and the source to 1280x720, the image will
+	be stretched to fit the source resolution. Works for any resolution
+	within the vimc limitations (even shrinking the image if necessary).
+	Exposes:
+
+	* 1 Pad sink
+	* 1 Pad source
+
+vimc-capture:
+	Exposes node /dev/videoX to allow userspace to capture the stream.
+	Exposes:
+
+	* 1 Pad sink
+	* 1 Pad source
+
+Module options
+--------------
+
+Vimc has a module parameter to configure the driver.
+
+* ``allocator=<unsigned int>``
+
+	memory allocator selection, default is 0. It specifies the way buffers
+	will be allocated.
+
+		- 0: vmalloc
+		- 1: dma-contig