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>

3 files changed, 152 insertions, 0 deletions

diff --git a/lib/tests/module/.gitignore b/lib/tests/module/.gitignore
new file mode 100644
index 000000000..8be7891b2
--- /dev/null
+++ b/lib/tests/module/.gitignore
@@ -0,0 +1,4 @@
+test_kallsyms_a.c
+test_kallsyms_b.c
+test_kallsyms_c.c
+test_kallsyms_d.c
diff --git a/lib/tests/module/Makefile b/lib/tests/module/Makefile
new file mode 100644
index 000000000..2f3e1a772
--- /dev/null
+++ b/lib/tests/module/Makefile
@@ -0,0 +1,14 @@
+obj-$(CONFIG_TEST_KALLSYMS_A) += test_kallsyms_a.o
+obj-$(CONFIG_TEST_KALLSYMS_B) += test_kallsyms_b.o
+obj-$(CONFIG_TEST_KALLSYMS_C) += test_kallsyms_c.o
+obj-$(CONFIG_TEST_KALLSYMS_D) += test_kallsyms_d.o
+
+quiet_cmd_gen_test_kallsyms = GEN     $@
+	cmd_gen_test_kallsyms = $< $@ \
+	$(CONFIG_TEST_KALLSYMS_NUMSYMS) \
+	$(CONFIG_TEST_KALLSYMS_SCALE_FACTOR)
+
+$(obj)/%.c: $(src)/gen_test_kallsyms.sh FORCE
+	$(call if_changed,gen_test_kallsyms)
+
+targets += $(foreach x, a b c d, test_kallsyms_$(x).c)
diff --git a/lib/tests/module/gen_test_kallsyms.sh b/lib/tests/module/gen_test_kallsyms.sh
new file mode 100755
index 000000000..31fe4ed63
--- /dev/null
+++ b/lib/tests/module/gen_test_kallsyms.sh
@@ -0,0 +1,134 @@
+#!/usr/bin/env bash
+
+TARGET=$(basename $1)
+DIR=lib/tests/module
+TARGET="$DIR/$TARGET"
+NUM_SYMS=$2
+SCALE_FACTOR=$3
+TEST_TYPE=$(echo $TARGET | sed -e 's|lib/tests/module/test_kallsyms_||g')
+TEST_TYPE=$(echo $TEST_TYPE | sed -e 's|.c||g')
+FIRST_B_LOOKUP=1
+
+if [[ $NUM_SYMS -gt 2 ]]; then
+	FIRST_B_LOOKUP=$((NUM_SYMS/2))
+fi
+
+gen_template_module_header()
+{
+	cat <<____END_MODULE
+// SPDX-License-Identifier: GPL-2.0-or-later OR copyleft-next-0.3.1
+/*
+ * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
+ *
+ * Automatically generated code for testing, do not edit manually.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+____END_MODULE
+}
+
+gen_num_syms()
+{
+	PREFIX=$1
+	NUM=$2
+	for i in $(seq 1 $NUM); do
+		printf "int auto_test_%s_%010d = 0;\n" $PREFIX $i
+		printf "EXPORT_SYMBOL_GPL(auto_test_%s_%010d);\n" $PREFIX $i
+	done
+	echo
+}
+
+gen_template_module_data_a()
+{
+	gen_num_syms a $1
+	cat <<____END_MODULE
+static int auto_runtime_test(void)
+{
+	return 0;
+}
+
+____END_MODULE
+}
+
+gen_template_module_data_b()
+{
+	printf "\nextern int auto_test_a_%010d;\n\n" $FIRST_B_LOOKUP
+	echo "static int auto_runtime_test(void)"
+	echo "{"
+	printf "\nreturn auto_test_a_%010d;\n" $FIRST_B_LOOKUP
+	echo "}"
+}
+
+gen_template_module_data_c()
+{
+	gen_num_syms c $1
+	cat <<____END_MODULE
+static int auto_runtime_test(void)
+{
+	return 0;
+}
+
+____END_MODULE
+}
+
+gen_template_module_data_d()
+{
+	gen_num_syms d $1
+	cat <<____END_MODULE
+static int auto_runtime_test(void)
+{
+	return 0;
+}
+
+____END_MODULE
+}
+
+gen_template_module_exit()
+{
+	cat <<____END_MODULE
+static int __init auto_test_module_init(void)
+{
+	return auto_runtime_test();
+}
+module_init(auto_test_module_init);
+
+static void __exit auto_test_module_exit(void)
+{
+}
+module_exit(auto_test_module_exit);
+
+MODULE_AUTHOR("Luis Chamberlain <mcgrof@kernel.org>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Test module for kallsyms");
+____END_MODULE
+}
+
+case $TEST_TYPE in
+	a)
+		gen_template_module_header > $TARGET
+		gen_template_module_data_a $NUM_SYMS >> $TARGET
+		gen_template_module_exit >> $TARGET
+		;;
+	b)
+		gen_template_module_header > $TARGET
+		gen_template_module_data_b >> $TARGET
+		gen_template_module_exit >> $TARGET
+		;;
+	c)
+		gen_template_module_header > $TARGET
+		gen_template_module_data_c $((NUM_SYMS * SCALE_FACTOR)) >> $TARGET
+		gen_template_module_exit >> $TARGET
+		;;
+	d)
+		gen_template_module_header > $TARGET
+		gen_template_module_data_d $((NUM_SYMS * SCALE_FACTOR * 2)) >> $TARGET
+		gen_template_module_exit >> $TARGET
+		;;
+	*)
+		;;
+esac