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, 111 insertions, 0 deletions

diff --git a/drivers/reset/reset-berlin.c b/drivers/reset/reset-berlin.c
new file mode 100644
index 000000000..578fe8670
--- /dev/null
+++ b/drivers/reset/reset-berlin.c
@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2014 Marvell Technology Group Ltd.
+ *
+ * Marvell Berlin reset driver
+ *
+ * Antoine Tenart <antoine.tenart@free-electrons.com>
+ * Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/reset-controller.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#define BERLIN_MAX_RESETS	32
+
+#define to_berlin_reset_priv(p)		\
+	container_of((p), struct berlin_reset_priv, rcdev)
+
+struct berlin_reset_priv {
+	struct regmap			*regmap;
+	struct reset_controller_dev	rcdev;
+};
+
+static int berlin_reset_reset(struct reset_controller_dev *rcdev,
+			      unsigned long id)
+{
+	struct berlin_reset_priv *priv = to_berlin_reset_priv(rcdev);
+	int offset = id >> 8;
+	int mask = BIT(id & 0x1f);
+
+	regmap_write(priv->regmap, offset, mask);
+
+	/* let the reset be effective */
+	udelay(10);
+
+	return 0;
+}
+
+static const struct reset_control_ops berlin_reset_ops = {
+	.reset	= berlin_reset_reset,
+};
+
+static int berlin_reset_xlate(struct reset_controller_dev *rcdev,
+			      const struct of_phandle_args *reset_spec)
+{
+	unsigned int offset, bit;
+
+	offset = reset_spec->args[0];
+	bit = reset_spec->args[1];
+
+	if (bit >= BERLIN_MAX_RESETS)
+		return -EINVAL;
+
+	return (offset << 8) | bit;
+}
+
+static int berlin2_reset_probe(struct platform_device *pdev)
+{
+	struct device_node *parent_np;
+	struct berlin_reset_priv *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	parent_np = of_get_parent(pdev->dev.of_node);
+	priv->regmap = syscon_node_to_regmap(parent_np);
+	of_node_put(parent_np);
+	if (IS_ERR(priv->regmap))
+		return PTR_ERR(priv->regmap);
+
+	priv->rcdev.owner = THIS_MODULE;
+	priv->rcdev.ops = &berlin_reset_ops;
+	priv->rcdev.of_node = pdev->dev.of_node;
+	priv->rcdev.of_reset_n_cells = 2;
+	priv->rcdev.of_xlate = berlin_reset_xlate;
+
+	return reset_controller_register(&priv->rcdev);
+}
+
+static const struct of_device_id berlin_reset_dt_match[] = {
+	{ .compatible = "marvell,berlin2-reset" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, berlin_reset_dt_match);
+
+static struct platform_driver berlin_reset_driver = {
+	.probe	= berlin2_reset_probe,
+	.driver	= {
+		.name = "berlin2-reset",
+		.of_match_table = berlin_reset_dt_match,
+	},
+};
+module_platform_driver(berlin_reset_driver);
+
+MODULE_AUTHOR("Antoine Tenart <antoine.tenart@free-electrons.com>");
+MODULE_AUTHOR("Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>");
+MODULE_DESCRIPTION("Synaptics Berlin reset controller");
+MODULE_LICENSE("GPL");