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, 201 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-test.c b/drivers/rtc/rtc-test.c
new file mode 100644
index 000000000..94f995feb
--- /dev/null
+++ b/drivers/rtc/rtc-test.c
@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * An RTC test device/driver
+ * Copyright (C) 2005 Tower Technologies
+ * Author: Alessandro Zummo <a.zummo@towertech.it>
+ */
+
+#include <linux/module.h>
+#include <linux/err.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+#define MAX_RTC_TEST 3
+
+struct rtc_test_data {
+	struct rtc_device *rtc;
+	time64_t offset;
+	struct timer_list alarm;
+	bool alarm_en;
+};
+
+static struct platform_device *pdev[MAX_RTC_TEST];
+
+static int test_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rtc_test_data *rtd = dev_get_drvdata(dev);
+	time64_t alarm;
+
+	alarm = (rtd->alarm.expires - jiffies) / HZ;
+	alarm += ktime_get_real_seconds() + rtd->offset;
+
+	rtc_time64_to_tm(alarm, &alrm->time);
+	alrm->enabled = rtd->alarm_en;
+
+	return 0;
+}
+
+static int test_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rtc_test_data *rtd = dev_get_drvdata(dev);
+	ktime_t timeout;
+	u64 expires;
+
+	timeout = rtc_tm_to_time64(&alrm->time) - ktime_get_real_seconds();
+	timeout -= rtd->offset;
+
+	timer_delete(&rtd->alarm);
+
+	expires = jiffies + timeout * HZ;
+	if (expires > U32_MAX)
+		expires = U32_MAX;
+
+	rtd->alarm.expires = expires;
+
+	if (alrm->enabled)
+		add_timer(&rtd->alarm);
+
+	rtd->alarm_en = alrm->enabled;
+
+	return 0;
+}
+
+static int test_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rtc_test_data *rtd = dev_get_drvdata(dev);
+
+	rtc_time64_to_tm(ktime_get_real_seconds() + rtd->offset, tm);
+
+	return 0;
+}
+
+static int test_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rtc_test_data *rtd = dev_get_drvdata(dev);
+
+	rtd->offset = rtc_tm_to_time64(tm) - ktime_get_real_seconds();
+
+	return 0;
+}
+
+static int test_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	struct rtc_test_data *rtd = dev_get_drvdata(dev);
+
+	rtd->alarm_en = enable;
+	if (enable)
+		add_timer(&rtd->alarm);
+	else
+		timer_delete(&rtd->alarm);
+
+	return 0;
+}
+
+static const struct rtc_class_ops test_rtc_ops_noalm = {
+	.read_time = test_rtc_read_time,
+	.set_time = test_rtc_set_time,
+	.alarm_irq_enable = test_rtc_alarm_irq_enable,
+};
+
+static const struct rtc_class_ops test_rtc_ops = {
+	.read_time = test_rtc_read_time,
+	.set_time = test_rtc_set_time,
+	.read_alarm = test_rtc_read_alarm,
+	.set_alarm = test_rtc_set_alarm,
+	.alarm_irq_enable = test_rtc_alarm_irq_enable,
+};
+
+static void test_rtc_alarm_handler(struct timer_list *t)
+{
+	struct rtc_test_data *rtd = timer_container_of(rtd, t, alarm);
+
+	rtc_update_irq(rtd->rtc, 1, RTC_AF | RTC_IRQF);
+}
+
+static int test_probe(struct platform_device *plat_dev)
+{
+	struct rtc_test_data *rtd;
+
+	rtd = devm_kzalloc(&plat_dev->dev, sizeof(*rtd), GFP_KERNEL);
+	if (!rtd)
+		return -ENOMEM;
+
+	platform_set_drvdata(plat_dev, rtd);
+
+	rtd->rtc = devm_rtc_allocate_device(&plat_dev->dev);
+	if (IS_ERR(rtd->rtc))
+		return PTR_ERR(rtd->rtc);
+
+	switch (plat_dev->id) {
+	case 0:
+		rtd->rtc->ops = &test_rtc_ops_noalm;
+		break;
+	default:
+		rtd->rtc->ops = &test_rtc_ops;
+		device_init_wakeup(&plat_dev->dev, true);
+	}
+
+	timer_setup(&rtd->alarm, test_rtc_alarm_handler, 0);
+	rtd->alarm.expires = 0;
+
+	return devm_rtc_register_device(rtd->rtc);
+}
+
+static struct platform_driver test_driver = {
+	.probe	= test_probe,
+	.driver = {
+		.name = "rtc-test",
+	},
+};
+
+static int __init test_init(void)
+{
+	int i, err;
+
+	err = platform_driver_register(&test_driver);
+	if (err)
+		return err;
+
+	err = -ENOMEM;
+	for (i = 0; i < MAX_RTC_TEST; i++) {
+		pdev[i] = platform_device_alloc("rtc-test", i);
+		if (!pdev[i])
+			goto exit_free_mem;
+	}
+
+	for (i = 0; i < MAX_RTC_TEST; i++) {
+		err = platform_device_add(pdev[i]);
+		if (err)
+			goto exit_device_del;
+	}
+
+	return 0;
+
+exit_device_del:
+	for (; i > 0; i--)
+		platform_device_del(pdev[i - 1]);
+
+exit_free_mem:
+	for (i = 0; i < MAX_RTC_TEST; i++)
+		platform_device_put(pdev[i]);
+
+	platform_driver_unregister(&test_driver);
+	return err;
+}
+
+static void __exit test_exit(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_RTC_TEST; i++)
+		platform_device_unregister(pdev[i]);
+
+	platform_driver_unregister(&test_driver);
+}
+
+MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");
+MODULE_DESCRIPTION("RTC test driver/device");
+MODULE_LICENSE("GPL v2");
+
+module_init(test_init);
+module_exit(test_exit);