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, 218 insertions, 0 deletions

diff --git a/drivers/mtd/maps/plat-ram.c b/drivers/mtd/maps/plat-ram.c
new file mode 100644
index 000000000..816111031
--- /dev/null
+++ b/drivers/mtd/maps/plat-ram.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* drivers/mtd/maps/plat-ram.c
+ *
+ * (c) 2004-2005 Simtec Electronics
+ *	http://www.simtec.co.uk/products/SWLINUX/
+ *	Ben Dooks <ben@simtec.co.uk>
+ *
+ * Generic platform device based RAM map
+*/
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/ioport.h>
+#include <linux/device.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+#include <linux/mtd/plat-ram.h>
+
+#include <asm/io.h>
+
+/* private structure for each mtd platform ram device created */
+
+struct platram_info {
+	struct device		*dev;
+	struct mtd_info		*mtd;
+	struct map_info		 map;
+	struct platdata_mtd_ram	*pdata;
+};
+
+/* to_platram_info()
+ *
+ * device private data to struct platram_info conversion
+*/
+
+static inline struct platram_info *to_platram_info(struct platform_device *dev)
+{
+	return platform_get_drvdata(dev);
+}
+
+/* platram_setrw
+ *
+ * call the platform device's set rw/ro control
+ *
+ * to = 0 => read-only
+ *    = 1 => read-write
+*/
+
+static inline void platram_setrw(struct platram_info *info, int to)
+{
+	if (info->pdata == NULL)
+		return;
+
+	if (info->pdata->set_rw != NULL)
+		(info->pdata->set_rw)(info->dev, to);
+}
+
+/* platram_remove
+ *
+ * called to remove the device from the driver's control
+*/
+
+static void platram_remove(struct platform_device *pdev)
+{
+	struct platram_info *info = to_platram_info(pdev);
+
+	dev_dbg(&pdev->dev, "removing device\n");
+
+	if (info == NULL)
+		return;
+
+	if (info->mtd) {
+		mtd_device_unregister(info->mtd);
+		map_destroy(info->mtd);
+	}
+
+	/* ensure ram is left read-only */
+
+	platram_setrw(info, PLATRAM_RO);
+
+	kfree(info);
+}
+
+/* platram_probe
+ *
+ * called from device drive system when a device matching our
+ * driver is found.
+*/
+
+static int platram_probe(struct platform_device *pdev)
+{
+	struct platdata_mtd_ram	*pdata;
+	struct platram_info *info;
+	struct resource *res;
+	int err = 0;
+
+	dev_dbg(&pdev->dev, "probe entered\n");
+
+	if (dev_get_platdata(&pdev->dev) == NULL) {
+		dev_err(&pdev->dev, "no platform data supplied\n");
+		err = -ENOENT;
+		goto exit_error;
+	}
+
+	pdata = dev_get_platdata(&pdev->dev);
+
+	info = kzalloc_obj(*info);
+	if (info == NULL) {
+		err = -ENOMEM;
+		goto exit_error;
+	}
+
+	platform_set_drvdata(pdev, info);
+
+	info->dev = &pdev->dev;
+	info->pdata = pdata;
+
+	/* get the resource for the memory mapping */
+	info->map.virt = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(info->map.virt)) {
+		err = PTR_ERR(info->map.virt);
+		goto exit_free;
+	}
+
+	dev_dbg(&pdev->dev, "got platform resource %p (0x%llx)\n", res,
+		(unsigned long long)res->start);
+
+	/* setup map parameters */
+
+	info->map.phys = res->start;
+	info->map.size = resource_size(res);
+	info->map.name = pdata->mapname != NULL ?
+			(char *)pdata->mapname : (char *)pdev->name;
+	info->map.bankwidth = pdata->bankwidth;
+
+	dev_dbg(&pdev->dev, "virt %p, %lu bytes\n", info->map.virt, info->map.size);
+
+	simple_map_init(&info->map);
+
+	dev_dbg(&pdev->dev, "initialised map, probing for mtd\n");
+
+	/* probe for the right mtd map driver
+	 * supplied by the platform_data struct */
+
+	if (pdata->map_probes) {
+		const char * const *map_probes = pdata->map_probes;
+
+		for ( ; !info->mtd && *map_probes; map_probes++)
+			info->mtd = do_map_probe(*map_probes , &info->map);
+	}
+	/* fallback to map_ram */
+	else
+		info->mtd = do_map_probe("map_ram", &info->map);
+
+	if (info->mtd == NULL) {
+		dev_err(&pdev->dev, "failed to probe for map_ram\n");
+		err = -ENOMEM;
+		goto exit_free;
+	}
+
+	info->mtd->dev.parent = &pdev->dev;
+
+	platram_setrw(info, PLATRAM_RW);
+
+	/* check to see if there are any available partitions, or whether
+	 * to add this device whole */
+
+	err = mtd_device_parse_register(info->mtd, pdata->probes, NULL,
+					pdata->partitions,
+					pdata->nr_partitions);
+	if (err) {
+		dev_err(&pdev->dev, "failed to register mtd device\n");
+		goto exit_free;
+	}
+
+	dev_info(&pdev->dev, "registered mtd device\n");
+
+	if (pdata->nr_partitions) {
+		/* add the whole device. */
+		err = mtd_device_register(info->mtd, NULL, 0);
+		if (err) {
+			dev_err(&pdev->dev,
+				"failed to register the entire device\n");
+			goto exit_free;
+		}
+	}
+
+	return 0;
+
+ exit_free:
+	platram_remove(pdev);
+ exit_error:
+	return err;
+}
+
+/* device driver info */
+
+/* work with hotplug and coldplug */
+MODULE_ALIAS("platform:mtd-ram");
+
+static struct platform_driver platram_driver = {
+	.probe		= platram_probe,
+	.remove		= platram_remove,
+	.driver		= {
+		.name	= "mtd-ram",
+	},
+};
+
+module_platform_driver(platram_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>");
+MODULE_DESCRIPTION("MTD platform RAM map driver");