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, 147 insertions, 0 deletions

diff --git a/drivers/hwmon/kbatt.c b/drivers/hwmon/kbatt.c
new file mode 100644
index 000000000..501b8f4de
--- /dev/null
+++ b/drivers/hwmon/kbatt.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 KEBA Industrial Automation GmbH
+ *
+ * Driver for KEBA battery monitoring controller FPGA IP core
+ */
+
+#include <linux/hwmon.h>
+#include <linux/io.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/auxiliary_bus.h>
+#include <linux/misc/keba.h>
+#include <linux/mutex.h>
+
+#define KBATT "kbatt"
+
+#define KBATT_CONTROL_REG		0x4
+#define   KBATT_CONTROL_BAT_TEST	0x01
+
+#define KBATT_STATUS_REG		0x8
+#define   KBATT_STATUS_BAT_OK		0x01
+
+#define KBATT_MAX_UPD_INTERVAL	(10 * HZ)
+#define KBATT_SETTLE_TIME_US	(100 * USEC_PER_MSEC)
+
+struct kbatt {
+	/* update lock */
+	struct mutex lock;
+	void __iomem *base;
+
+	unsigned long next_update; /* in jiffies */
+	bool alarm;
+};
+
+static bool kbatt_alarm(struct kbatt *kbatt)
+{
+	mutex_lock(&kbatt->lock);
+
+	if (!kbatt->next_update || time_after(jiffies, kbatt->next_update)) {
+		/* switch load on */
+		iowrite8(KBATT_CONTROL_BAT_TEST,
+			 kbatt->base + KBATT_CONTROL_REG);
+
+		/* wait some time to let things settle */
+		fsleep(KBATT_SETTLE_TIME_US);
+
+		/* check battery state */
+		if (ioread8(kbatt->base + KBATT_STATUS_REG) &
+		    KBATT_STATUS_BAT_OK)
+			kbatt->alarm = false;
+		else
+			kbatt->alarm = true;
+
+		/* switch load off */
+		iowrite8(0, kbatt->base + KBATT_CONTROL_REG);
+
+		kbatt->next_update = jiffies + KBATT_MAX_UPD_INTERVAL;
+	}
+
+	mutex_unlock(&kbatt->lock);
+
+	return kbatt->alarm;
+}
+
+static int kbatt_read(struct device *dev, enum hwmon_sensor_types type,
+		      u32 attr, int channel, long *val)
+{
+	struct kbatt *kbatt = dev_get_drvdata(dev);
+
+	*val = kbatt_alarm(kbatt) ? 1 : 0;
+
+	return 0;
+}
+
+static umode_t kbatt_is_visible(const void *data, enum hwmon_sensor_types type,
+				u32 attr, int channel)
+{
+	if (channel == 0 && attr == hwmon_in_min_alarm)
+		return 0444;
+
+	return 0;
+}
+
+static const struct hwmon_channel_info *kbatt_info[] = {
+	HWMON_CHANNEL_INFO(in,
+			   /* 0: input minimum alarm channel */
+			   HWMON_I_MIN_ALARM),
+	NULL
+};
+
+static const struct hwmon_ops kbatt_hwmon_ops = {
+	.is_visible = kbatt_is_visible,
+	.read = kbatt_read,
+};
+
+static const struct hwmon_chip_info kbatt_chip_info = {
+	.ops = &kbatt_hwmon_ops,
+	.info = kbatt_info,
+};
+
+static int kbatt_probe(struct auxiliary_device *auxdev,
+		       const struct auxiliary_device_id *id)
+{
+	struct keba_batt_auxdev *kbatt_auxdev =
+		container_of(auxdev, struct keba_batt_auxdev, auxdev);
+	struct device *dev = &auxdev->dev;
+	struct device *hwmon_dev;
+	struct kbatt *kbatt;
+	int retval;
+
+	kbatt = devm_kzalloc(dev, sizeof(*kbatt), GFP_KERNEL);
+	if (!kbatt)
+		return -ENOMEM;
+
+	retval = devm_mutex_init(dev, &kbatt->lock);
+	if (retval)
+		return retval;
+
+	kbatt->base = devm_ioremap_resource(dev, &kbatt_auxdev->io);
+	if (IS_ERR(kbatt->base))
+		return PTR_ERR(kbatt->base);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, KBATT, kbatt,
+							 &kbatt_chip_info,
+							 NULL);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct auxiliary_device_id kbatt_devtype_aux[] = {
+	{ .name = "keba.batt" },
+	{}
+};
+MODULE_DEVICE_TABLE(auxiliary, kbatt_devtype_aux);
+
+static struct auxiliary_driver kbatt_driver_aux = {
+	.name = KBATT,
+	.id_table = kbatt_devtype_aux,
+	.probe = kbatt_probe,
+};
+module_auxiliary_driver(kbatt_driver_aux);
+
+MODULE_AUTHOR("Petar Bojanic <boja@keba.com>");
+MODULE_AUTHOR("Gerhard Engleder <eg@keba.com>");
+MODULE_DESCRIPTION("KEBA battery monitoring controller driver");
+MODULE_LICENSE("GPL");