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, 90 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-auxdisplay-linedisp b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
new file mode 100644
index 000000000..55f1b559e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
@@ -0,0 +1,90 @@
+What:		/sys/.../message
+Date:		October 2021
+KernelVersion:	5.16
+Description:
+		Controls the text message displayed on character line displays.
+
+		Reading returns the current message with a trailing newline.
+		Writing updates the displayed message. Messages longer than the
+		display width will automatically scroll. Trailing newlines in
+		input are automatically trimmed.
+
+		Writing an empty string clears the display.
+
+		Example:
+		  echo "Hello World" > message
+		  cat message			# Returns "Hello World\n"
+
+What:		/sys/.../num_chars
+Date:		November 2025
+KernelVersion:	6.18
+Contact:	Jean-François Lessard <jefflessard3@gmail.com>
+Description:
+		Read-only attribute showing the character width capacity of
+		the line display device. Messages longer than this will scroll.
+
+		Example:
+		  cat num_chars		# Returns "16\n" for 16-char display
+
+What:		/sys/.../scroll_step_ms
+Date:		October 2021
+KernelVersion:	5.16
+Description:
+		Controls the scrolling speed for messages longer than the display
+		width, specified in milliseconds per scroll step.
+
+		Setting to 0 disables scrolling. Default is 500ms.
+
+		Example:
+		  echo "250" > scroll_step_ms	# 4Hz scrolling
+		  cat scroll_step_ms		# Returns "250\n"
+
+What:		/sys/.../map_seg7
+Date:		January 2024
+KernelVersion:	6.9
+Description:
+		Read/write binary blob representing the ASCII-to-7-segment
+		display conversion table used by the linedisp driver, as defined
+		by struct seg7_conversion_map in <linux/map_to_7segment.h>.
+
+		Only visible on displays with 7-segment capability.
+
+		This attribute is not human-readable. Writes must match the
+		struct size exactly, else -EINVAL is returned; reads return the
+		entire mapping as a binary blob.
+
+		This interface and its implementation match existing conventions
+		used in segment-mapped display drivers since 2005.
+
+		ABI note: This style of binary sysfs attribute *is an exception*
+		to current "one value per file, text only" sysfs rules, for
+		historical compatibility and driver uniformity. New drivers are
+		discouraged from introducing additional binary sysfs ABIs.
+
+		Reference interface guidance:
+		- include/uapi/linux/map_to_7segment.h
+
+What:		/sys/.../map_seg14
+Date:		January 2024
+KernelVersion:	6.9
+Description:
+		Read/write binary blob representing the ASCII-to-14-segment
+		display conversion table used by the linedisp driver, as defined
+		by struct seg14_conversion_map in <linux/map_to_14segment.h>.
+
+		Only visible on displays with 14-segment capability.
+
+		This attribute is not human-readable. Writes must match the
+		struct size exactly, else -EINVAL is returned; reads return the
+		entire mapping as a binary blob.
+
+		This interface and its implementation match existing conventions
+		used by segment-mapped display drivers since 2005.
+
+		ABI note: This style of binary sysfs attribute *is an exception*
+		to current "one value per file, text only" sysfs rules, for
+		historical compatibility and driver uniformity. New drivers are
+		discouraged from introducing additional binary sysfs ABIs.
+
+		Reference interface guidance:
+		- include/uapi/linux/map_to_14segment.h