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, 135 insertions, 0 deletions

diff --git a/drivers/video/cmdline.c b/drivers/video/cmdline.c
new file mode 100644
index 000000000..49ee3fb49
--- /dev/null
+++ b/drivers/video/cmdline.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Based on the fbdev code in drivers/video/fbdev/core/fb_cmdline:
+ *
+ *  Copyright (C) 2014 Intel Corp
+ *  Copyright (C) 1994 Martin Schaller
+ *
+ *	2001 - Documented with DocBook
+ *	- Brad Douglas <brad@neruo.com>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ *
+ * Authors:
+ *    Daniel Vetter <daniel.vetter@ffwll.ch>
+ */
+
+#include <linux/fb.h> /* for FB_MAX */
+#include <linux/init.h>
+
+#include <video/cmdline.h>
+
+/*
+ * FB_MAX is the maximum number of framebuffer devices and also
+ * the maximum number of video= parameters. Although not directly
+ * related to each other, it makes sense to keep it that way.
+ */
+static const char *video_options[FB_MAX] __read_mostly;
+static const char *video_option __read_mostly;
+static int video_of_only __read_mostly;
+
+static const char *__video_get_option_string(const char *name)
+{
+	const char *options = NULL;
+	size_t name_len = 0;
+
+	if (name)
+		name_len = strlen(name);
+
+	if (name_len) {
+		unsigned int i;
+		const char *opt;
+
+		for (i = 0; i < ARRAY_SIZE(video_options); ++i) {
+			if (!video_options[i])
+				continue;
+			if (video_options[i][0] == '\0')
+				continue;
+			opt = video_options[i];
+			if (!strncmp(opt, name, name_len) && opt[name_len] == ':')
+				options = opt + name_len + 1;
+		}
+	}
+
+	/* No match, return global options */
+	if (!options)
+		options = video_option;
+
+	return options;
+}
+
+/**
+ * video_get_options - get kernel boot parameters
+ * @name:	name of the output as it would appear in the boot parameter
+ *		line (video=<name>:<options>)
+ *
+ * Looks up the video= options for the given name. Names are connector
+ * names with DRM, or driver names with fbdev. If no video option for
+ * the name has been specified, the function returns the global video=
+ * setting. A @name of NULL always returns the global video setting.
+ *
+ * Returns:
+ * The string of video options for the given name, or NULL if no video
+ * option has been specified.
+ */
+const char *video_get_options(const char *name)
+{
+	return __video_get_option_string(name);
+}
+EXPORT_SYMBOL(video_get_options);
+
+#if IS_ENABLED(CONFIG_FB_CORE)
+bool __video_get_options(const char *name, const char **options, bool is_of)
+{
+	bool enabled = true;
+	const char *opt = NULL;
+
+	if (video_of_only && !is_of)
+		enabled = false;
+
+	opt = __video_get_option_string(name);
+
+	if (options)
+		*options = opt;
+
+	return enabled;
+}
+EXPORT_SYMBOL(__video_get_options);
+#endif
+
+/*
+ * Process command line options for video adapters. This function is
+ * a __setup and __init function. It only stores the options. Drivers
+ * have to call video_get_options() as necessary.
+ */
+static int __init video_setup(char *options)
+{
+	if (!options || !*options)
+		goto out;
+
+	if (!strncmp(options, "ofonly", 6)) {
+		video_of_only = true;
+		goto out;
+	}
+
+	if (strchr(options, ':')) {
+		/* named */
+		size_t i;
+
+		for (i = 0; i < ARRAY_SIZE(video_options); i++) {
+			if (!video_options[i]) {
+				video_options[i] = options;
+				break;
+			}
+		}
+	} else {
+		/* global */
+		video_option = options;
+	}
+
+out:
+	return 1;
+}
+__setup("video=", video_setup);