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, 129 insertions, 0 deletions

diff --git a/scripts/show_delta b/scripts/show_delta
new file mode 100755
index 000000000..3755b6c6e
--- /dev/null
+++ b/scripts/show_delta
@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# show_deltas: Read list of printk messages instrumented with
+# time data, and format with time deltas.
+#
+# Also, you can show the times relative to a fixed point.
+#
+# Copyright 2003 Sony Corporation
+#
+
+import sys
+import string
+
+def usage():
+	print ("""usage: show_delta [<options>] <filename>
+
+This program parses the output from a set of printk message lines which
+have time data prefixed because the CONFIG_PRINTK_TIME option is set, or
+the kernel command line option "time" is specified. When run with no
+options, the time information is converted to show the time delta between
+each printk line and the next.  When run with the '-b' option, all times
+are relative to a single (base) point in time.
+
+Options:
+  -h            Show this usage help.
+  -b <base>	Specify a base for time references.
+		<base> can be a number or a string.
+		If it is a string, the first message line
+		which matches (at the beginning of the
+		line) is used as the time reference.
+
+ex: $ dmesg >timefile
+    $ show_delta -b NET4 timefile
+
+will show times relative to the line in the kernel output
+starting with "NET4".
+""")
+	sys.exit(1)
+
+# returns a tuple containing the seconds and text for each message line
+# seconds is returned as a float
+# raise an exception if no timing data was found
+def get_time(line):
+	if line[0]!="[":
+		raise ValueError
+
+	# split on closing bracket
+	(time_str, rest) = string.split(line[1:],']',1)
+	time = string.atof(time_str)
+
+	#print "time=", time
+	return (time, rest)
+
+
+# average line looks like:
+# [    0.084282] VFS: Mounted root (romfs filesystem) readonly
+# time data is expressed in seconds.useconds,
+# convert_line adds a delta for each line
+last_time = 0.0
+def convert_line(line, base_time):
+	global last_time
+
+	try:
+		(time, rest) = get_time(line)
+	except:
+		# if any problem parsing time, don't convert anything
+		return line
+
+	if base_time:
+		# show time from base
+		delta = time - base_time
+	else:
+		# just show time from last line
+		delta = time - last_time
+		last_time = time
+
+	return ("[%5.6f < %5.6f >]" % (time, delta)) + rest
+
+def main():
+	base_str = ""
+	filein = ""
+	for arg in sys.argv[1:]:
+		if arg=="-b":
+			base_str = sys.argv[sys.argv.index("-b")+1]
+		elif arg=="-h":
+			usage()
+		else:
+			filein = arg
+
+	if not filein:
+		usage()
+
+	try:
+		lines = open(filein,"r").readlines()
+	except:
+		print ("Problem opening file: %s" % filein)
+		sys.exit(1)
+
+	if base_str:
+		print ('base= "%s"' % base_str)
+		# assume a numeric base.  If that fails, try searching
+		# for a matching line.
+		try:
+			base_time = float(base_str)
+		except:
+			# search for line matching <base> string
+			found = 0
+			for line in lines:
+				try:
+					(time, rest) = get_time(line)
+				except:
+					continue
+				if string.find(rest, base_str)==1:
+					base_time = time
+					found = 1
+					# stop at first match
+					break
+			if not found:
+				print ('Couldn\'t find line matching base pattern "%s"' % base_str)
+				sys.exit(1)
+	else:
+		base_time = 0.0
+
+	for line in lines:
+		print (convert_line(line, base_time),)
+
+if __name__ == "__main__":
+	main()