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, 127 insertions, 0 deletions

diff --git a/drivers/reset/reset-ath79.c b/drivers/reset/reset-ath79.c
new file mode 100644
index 000000000..1a2c0f8a5
--- /dev/null
+++ b/drivers/reset/reset-ath79.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * AR71xx Reset Controller Driver
+ * Author: Alban Bedel
+ *
+ * Copyright (C) 2015 Alban Bedel <albeu@free.fr>
+ */
+
+#include <linux/io.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+#include <linux/reboot.h>
+
+struct ath79_reset {
+	struct reset_controller_dev rcdev;
+	void __iomem *base;
+	spinlock_t lock;
+};
+
+#define FULL_CHIP_RESET 24
+
+static int ath79_reset_update(struct reset_controller_dev *rcdev,
+			unsigned long id, bool assert)
+{
+	struct ath79_reset *ath79_reset =
+		container_of(rcdev, struct ath79_reset, rcdev);
+	unsigned long flags;
+	u32 val;
+
+	spin_lock_irqsave(&ath79_reset->lock, flags);
+	val = readl(ath79_reset->base);
+	if (assert)
+		val |= BIT(id);
+	else
+		val &= ~BIT(id);
+	writel(val, ath79_reset->base);
+	spin_unlock_irqrestore(&ath79_reset->lock, flags);
+
+	return 0;
+}
+
+static int ath79_reset_assert(struct reset_controller_dev *rcdev,
+			unsigned long id)
+{
+	return ath79_reset_update(rcdev, id, true);
+}
+
+static int ath79_reset_deassert(struct reset_controller_dev *rcdev,
+				unsigned long id)
+{
+	return ath79_reset_update(rcdev, id, false);
+}
+
+static int ath79_reset_status(struct reset_controller_dev *rcdev,
+			unsigned long id)
+{
+	struct ath79_reset *ath79_reset =
+		container_of(rcdev, struct ath79_reset, rcdev);
+	u32 val;
+
+	val = readl(ath79_reset->base);
+
+	return !!(val & BIT(id));
+}
+
+static const struct reset_control_ops ath79_reset_ops = {
+	.assert = ath79_reset_assert,
+	.deassert = ath79_reset_deassert,
+	.status = ath79_reset_status,
+};
+
+static int ath79_reset_restart_handler(struct sys_off_data *data)
+{
+	struct ath79_reset *ath79_reset = data->cb_data;
+
+	ath79_reset_assert(&ath79_reset->rcdev, FULL_CHIP_RESET);
+
+	return NOTIFY_DONE;
+}
+
+static int ath79_reset_probe(struct platform_device *pdev)
+{
+	struct ath79_reset *ath79_reset;
+	int err;
+
+	ath79_reset = devm_kzalloc(&pdev->dev,
+				sizeof(*ath79_reset), GFP_KERNEL);
+	if (!ath79_reset)
+		return -ENOMEM;
+
+	ath79_reset->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(ath79_reset->base))
+		return PTR_ERR(ath79_reset->base);
+
+	spin_lock_init(&ath79_reset->lock);
+	ath79_reset->rcdev.ops = &ath79_reset_ops;
+	ath79_reset->rcdev.owner = THIS_MODULE;
+	ath79_reset->rcdev.of_node = pdev->dev.of_node;
+	ath79_reset->rcdev.of_reset_n_cells = 1;
+	ath79_reset->rcdev.nr_resets = 32;
+
+	err = devm_reset_controller_register(&pdev->dev, &ath79_reset->rcdev);
+	if (err)
+		return err;
+
+	err = devm_register_restart_handler(&pdev->dev, ath79_reset_restart_handler, ath79_reset);
+	if (err)
+		dev_warn(&pdev->dev, "Failed to register restart handler\n");
+
+	return 0;
+}
+
+static const struct of_device_id ath79_reset_dt_ids[] = {
+	{ .compatible = "qca,ar7100-reset", },
+	{ },
+};
+
+static struct platform_driver ath79_reset_driver = {
+	.probe	= ath79_reset_probe,
+	.driver = {
+		.name			= "ath79-reset",
+		.of_match_table		= ath79_reset_dt_ids,
+		.suppress_bind_attrs	= true,
+	},
+};
+builtin_platform_driver(ath79_reset_driver);