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, 217 insertions, 0 deletions

diff --git a/drivers/hwmon/lm70.c b/drivers/hwmon/lm70.c
new file mode 100644
index 000000000..8b525725f
--- /dev/null
+++ b/drivers/hwmon/lm70.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * lm70.c
+ *
+ * The LM70 is a temperature sensor chip from National Semiconductor (NS).
+ * Copyright (C) 2006 Kaiwan N Billimoria <kaiwan@designergraphix.com>
+ *
+ * The LM70 communicates with a host processor via an SPI/Microwire Bus
+ * interface. The complete datasheet is available at TI's website
+ * here:
+ * https://www.ti.com/product/LM70
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/sysfs.h>
+#include <linux/hwmon.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/property.h>
+#include <linux/spi/spi.h>
+#include <linux/slab.h>
+
+#define DRVNAME		"lm70"
+
+#define LM70_CHIP_LM70		0	/* original NS LM70 */
+#define LM70_CHIP_TMP121	1	/* TI TMP121/TMP123 */
+#define LM70_CHIP_LM71		2	/* NS LM71 */
+#define LM70_CHIP_LM74		3	/* NS LM74 */
+#define LM70_CHIP_TMP122	4	/* TI TMP122/TMP124 */
+#define LM70_CHIP_TMP125	5	/* TI TMP125 */
+
+struct lm70 {
+	struct spi_device *spi;
+	struct mutex lock;
+	unsigned int chip;
+};
+
+/* sysfs hook function */
+static ssize_t temp1_input_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct lm70 *p_lm70 = dev_get_drvdata(dev);
+	struct spi_device *spi = p_lm70->spi;
+	int status, val = 0;
+	u8 rxbuf[2];
+	s16 raw = 0;
+
+	if (mutex_lock_interruptible(&p_lm70->lock))
+		return -ERESTARTSYS;
+
+	/*
+	 * spi_read() requires a DMA-safe buffer; so we use
+	 * spi_write_then_read(), transmitting 0 bytes.
+	 */
+	status = spi_write_then_read(spi, NULL, 0, &rxbuf[0], 2);
+	if (status < 0) {
+		dev_warn(dev, "spi_write_then_read failed with status %d\n",
+			 status);
+		goto out;
+	}
+	raw = (rxbuf[0] << 8) + rxbuf[1];
+	dev_dbg(dev, "rxbuf[0] : 0x%02x rxbuf[1] : 0x%02x raw=0x%04x\n",
+		rxbuf[0], rxbuf[1], raw);
+
+	/*
+	 * LM70:
+	 * The "raw" temperature read into rxbuf[] is a 16-bit signed 2's
+	 * complement value. Only the MSB 11 bits (1 sign + 10 temperature
+	 * bits) are meaningful; the LSB 5 bits are to be discarded.
+	 * See the datasheet.
+	 *
+	 * Further, each bit represents 0.25 degrees Celsius; so, multiply
+	 * by 0.25. Also multiply by 1000 to represent in millidegrees
+	 * Celsius.
+	 * So it's equivalent to multiplying by 0.25 * 1000 = 250.
+	 *
+	 * LM74 and TMP121/TMP122/TMP123/TMP124:
+	 * 13 bits of 2's complement data, discard LSB 3 bits,
+	 * resolution 0.0625 degrees celsius.
+	 *
+	 * LM71:
+	 * 14 bits of 2's complement data, discard LSB 2 bits,
+	 * resolution 0.0312 degrees celsius.
+	 *
+	 * TMP125:
+	 * MSB/D15 is a leading zero. D14 is the sign-bit. This is
+	 * followed by 9 temperature bits (D13..D5) in 2's complement
+	 * data format with a resolution of 0.25 degrees celsius per unit.
+	 * LSB 5 bits (D4..D0) share the same value as D5 and get discarded.
+	 */
+	switch (p_lm70->chip) {
+	case LM70_CHIP_LM70:
+		val = ((int)raw / 32) * 250;
+		break;
+
+	case LM70_CHIP_TMP121:
+	case LM70_CHIP_TMP122:
+	case LM70_CHIP_LM74:
+		val = ((int)raw / 8) * 625 / 10;
+		break;
+
+	case LM70_CHIP_LM71:
+		val = ((int)raw / 4) * 3125 / 100;
+		break;
+
+	case LM70_CHIP_TMP125:
+		val = (sign_extend32(raw, 14) / 32) * 250;
+		break;
+	}
+
+	status = sprintf(buf, "%d\n", val); /* millidegrees Celsius */
+out:
+	mutex_unlock(&p_lm70->lock);
+	return status;
+}
+
+static DEVICE_ATTR_RO(temp1_input);
+
+static struct attribute *lm70_attrs[] = {
+	&dev_attr_temp1_input.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(lm70);
+
+/*----------------------------------------------------------------------*/
+
+#ifdef CONFIG_OF
+static const struct of_device_id lm70_of_ids[] = {
+	{
+		.compatible = "ti,lm70",
+		.data = (void *) LM70_CHIP_LM70,
+	},
+	{
+		.compatible = "ti,tmp121",
+		.data = (void *) LM70_CHIP_TMP121,
+	},
+	{
+		.compatible = "ti,tmp122",
+		.data = (void *) LM70_CHIP_TMP122,
+	},
+	{
+		.compatible = "ti,tmp125",
+		.data = (void *) LM70_CHIP_TMP125,
+	},
+	{
+		.compatible = "ti,lm71",
+		.data = (void *) LM70_CHIP_LM71,
+	},
+	{
+		.compatible = "ti,lm74",
+		.data = (void *) LM70_CHIP_LM74,
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, lm70_of_ids);
+#endif
+
+static int lm70_probe(struct spi_device *spi)
+{
+	struct device *hwmon_dev;
+	struct lm70 *p_lm70;
+	int chip;
+
+	chip = (kernel_ulong_t)spi_get_device_match_data(spi);
+
+	/* signaling is SPI_MODE_0 */
+	if ((spi->mode & SPI_MODE_X_MASK) != SPI_MODE_0)
+		return -EINVAL;
+
+	/* NOTE:  we assume 8-bit words, and convert to 16 bits manually */
+
+	p_lm70 = devm_kzalloc(&spi->dev, sizeof(*p_lm70), GFP_KERNEL);
+	if (!p_lm70)
+		return -ENOMEM;
+
+	mutex_init(&p_lm70->lock);
+	p_lm70->chip = chip;
+	p_lm70->spi = spi;
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(&spi->dev,
+							   spi->modalias,
+							   p_lm70, lm70_groups);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct spi_device_id lm70_ids[] = {
+	{ "lm70",   LM70_CHIP_LM70 },
+	{ "tmp121", LM70_CHIP_TMP121 },
+	{ "tmp122", LM70_CHIP_TMP122 },
+	{ "tmp125", LM70_CHIP_TMP125 },
+	{ "lm71",   LM70_CHIP_LM71 },
+	{ "lm74",   LM70_CHIP_LM74 },
+	{ },
+};
+MODULE_DEVICE_TABLE(spi, lm70_ids);
+
+static struct spi_driver lm70_driver = {
+	.driver = {
+		.name	= "lm70",
+		.of_match_table	= of_match_ptr(lm70_of_ids),
+	},
+	.id_table = lm70_ids,
+	.probe	= lm70_probe,
+};
+
+module_spi_driver(lm70_driver);
+
+MODULE_AUTHOR("Kaiwan N Billimoria");
+MODULE_DESCRIPTION("NS LM70 and compatibles Linux driver");
+MODULE_LICENSE("GPL");