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, 116 insertions, 0 deletions

diff --git a/scripts/dummy-tools/gcc b/scripts/dummy-tools/gcc
new file mode 100755
index 000000000..e6c41427c
--- /dev/null
+++ b/scripts/dummy-tools/gcc
@@ -0,0 +1,116 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG
+# options your compiler does not support. This works well if you configure and
+# build the kernel on the same host machine.
+#
+# It is inconvenient if you prepare the .config that is carried to a different
+# build environment (typically this happens when you package the kernel for
+# distros) because using a different compiler potentially produces different
+# CONFIG options than the real build environment. So, you probably want to make
+# as many options visible as possible. In other words, you need to create a
+# super-set of CONFIG options that cover any build environment. If some of the
+# CONFIG options turned out to be unsupported on the build machine, they are
+# automatically disabled by the nature of Kconfig.
+#
+# However, it is not feasible to get a full-featured compiler for every arch.
+# Hence these dummy toolchains to make all compiler tests pass.
+#
+# Usage:
+#
+# From the top directory of the source tree, run
+#
+#   $ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig
+#
+# Most of compiler features are tested by cc-option, which simply checks the
+# exit code of $(CC). This script does nothing and just exits with 0 in most
+# cases. So, $(cc-option, ...) is evaluated as 'y'.
+#
+# This scripts caters to more checks; handle --version and pre-process __GNUC__
+# etc. to pretend to be GCC, and also do right things to satisfy some scripts.
+
+# Check if the first parameter appears in the rest. Succeeds if found.
+# This helper is useful if a particular option was passed to this script.
+# Typically used like this:
+#   arg_contain <word-you-are-searching-for> "$@"
+arg_contain ()
+{
+	search="$1"
+	shift
+
+	while [ $# -gt 0 ]
+	do
+		if [ "$search" = "$1" ]; then
+			return 0
+		fi
+		shift
+	done
+
+	return 1
+}
+
+# To set CONFIG_CC_IS_GCC=y
+if arg_contain --version "$@"; then
+	echo "gcc (scripts/dummy-tools/gcc)"
+	exit 0
+fi
+
+if arg_contain -E "$@"; then
+	# For scripts/cc-version.sh; This emulates GCC 20.0.0
+	if arg_contain - "$@"; then
+		sed -n '/^GCC/{s/__GNUC__/20/; s/__GNUC_MINOR__/0/; s/__GNUC_PATCHLEVEL__/0/; p;}; s/__LONG_DOUBLE_128__/1/ p'
+		exit 0
+	else
+		echo "no input files" >&2
+		exit 1
+	fi
+fi
+
+# To set CONFIG_AS_IS_GNU
+if arg_contain -Wa,--version "$@"; then
+	echo "GNU assembler (scripts/dummy-tools) 2.50"
+	exit 0
+fi
+
+if arg_contain -S "$@"; then
+	# For scripts/gcc-x86-*-has-stack-protector.sh
+	if arg_contain -fstack-protector "$@"; then
+		if arg_contain -mstack-protector-guard-reg=fs "$@"; then
+			echo "%fs"
+		else
+			echo "%gs"
+		fi
+		exit 0
+	fi
+
+	# For arch/powerpc/tools/gcc-check-mprofile-kernel.sh
+	if arg_contain -m64 "$@" && arg_contain -mprofile-kernel "$@"; then
+		if ! test -t 0 && ! grep -q notrace; then
+			echo "_mcount"
+		fi
+		exit 0
+	fi
+
+	# For arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
+	if arg_contain -m64 "$@" && arg_contain -fpatchable-function-entry=2 "$@"; then
+		echo "func:"
+		echo ".section __patchable_function_entries"
+		echo ".localentry"
+		echo "  nop"
+		echo "  nop"
+		exit 0
+	fi
+fi
+
+# To set GCC_PLUGINS
+if arg_contain -print-file-name=plugin "$@"; then
+	# Use $0 to find the in-tree dummy directory
+	echo "$(dirname "$(readlink -f "$0")")/dummy-plugin-dir"
+	exit 0
+fi
+
+# inverted return value
+if arg_contain -D__SIZEOF_INT128__=0 "$@"; then
+	exit 1
+fi