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, 154 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max6902.c b/drivers/rtc/rtc-max6902.c
new file mode 100644
index 000000000..daaeb6fb6
--- /dev/null
+++ b/drivers/rtc/rtc-max6902.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* drivers/rtc/rtc-max6902.c
+ *
+ * Copyright (C) 2006 8D Technologies inc.
+ * Copyright (C) 2004 Compulab Ltd.
+ *
+ * Driver for MAX6902 spi RTC
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+#define MAX6902_REG_SECONDS		0x01
+#define MAX6902_REG_MINUTES		0x03
+#define MAX6902_REG_HOURS		0x05
+#define MAX6902_REG_DATE		0x07
+#define MAX6902_REG_MONTH		0x09
+#define MAX6902_REG_DAY			0x0B
+#define MAX6902_REG_YEAR		0x0D
+#define MAX6902_REG_CONTROL		0x0F
+#define MAX6902_REG_CENTURY		0x13
+
+static int max6902_set_reg(struct device *dev, unsigned char address,
+				unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	/* MSB must be '0' to write */
+	buf[0] = address & 0x7f;
+	buf[1] = data;
+
+	return spi_write_then_read(spi, buf, 2, NULL, 0);
+}
+
+static int max6902_get_reg(struct device *dev, unsigned char address,
+				unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	/* Set MSB to indicate read */
+	*data = address | 0x80;
+
+	return spi_write_then_read(spi, data, 1, data, 1);
+}
+
+static int max6902_read_time(struct device *dev, struct rtc_time *dt)
+{
+	int err, century;
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[8];
+
+	buf[0] = 0xbf;	/* Burst read */
+
+	err = spi_write_then_read(spi, buf, 1, buf, 8);
+	if (err != 0)
+		return err;
+
+	/* The chip sends data in this order:
+	 * Seconds, Minutes, Hours, Date, Month, Day, Year */
+	dt->tm_sec	= bcd2bin(buf[0]);
+	dt->tm_min	= bcd2bin(buf[1]);
+	dt->tm_hour	= bcd2bin(buf[2]);
+	dt->tm_mday	= bcd2bin(buf[3]);
+	dt->tm_mon	= bcd2bin(buf[4]) - 1;
+	dt->tm_wday	= bcd2bin(buf[5]);
+	dt->tm_year	= bcd2bin(buf[6]);
+
+	/* Read century */
+	err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]);
+	if (err != 0)
+		return err;
+
+	century = bcd2bin(buf[0]) * 100;
+
+	dt->tm_year += century;
+	dt->tm_year -= 1900;
+
+	return 0;
+}
+
+static int max6902_set_time(struct device *dev, struct rtc_time *dt)
+{
+	dt->tm_year = dt->tm_year + 1900;
+
+	/* Remove write protection */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0);
+
+	max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec));
+	max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min));
+	max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour));
+
+	max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday));
+	max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1));
+	max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday));
+	max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100));
+	max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100));
+
+	/* Compulab used a delay here. However, the datasheet
+	 * does not mention a delay being required anywhere... */
+	/* delay(2000); */
+
+	/* Write protect */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80);
+
+	return 0;
+}
+
+static const struct rtc_class_ops max6902_rtc_ops = {
+	.read_time	= max6902_read_time,
+	.set_time	= max6902_set_time,
+};
+
+static int max6902_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char tmp;
+	int res;
+
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp);
+	if (res != 0)
+		return res;
+
+	rtc = devm_rtc_device_register(&spi->dev, "max6902",
+				&max6902_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+	return 0;
+}
+
+static struct spi_driver max6902_driver = {
+	.driver = {
+		.name	= "rtc-max6902",
+	},
+	.probe	= max6902_probe,
+};
+
+module_spi_driver(max6902_driver);
+
+MODULE_DESCRIPTION("max6902 spi RTC driver");
+MODULE_AUTHOR("Raphael Assenat");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-max6902");