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, 126 insertions, 0 deletions

diff --git a/drivers/reset/reset-brcmstb.c b/drivers/reset/reset-brcmstb.c
new file mode 100644
index 000000000..810fe7645
--- /dev/null
+++ b/drivers/reset/reset-brcmstb.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Broadcom STB generic reset controller for SW_INIT style reset controller
+ *
+ * Author: Florian Fainelli <f.fainelli@gmail.com>
+ * Copyright (C) 2018 Broadcom
+ */
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+#include <linux/types.h>
+
+struct brcmstb_reset {
+	void __iomem *base;
+	struct reset_controller_dev rcdev;
+};
+
+#define SW_INIT_SET		0x00
+#define SW_INIT_CLEAR		0x04
+#define SW_INIT_STATUS		0x08
+
+#define SW_INIT_BIT(id)		BIT((id) & 0x1f)
+#define SW_INIT_BANK(id)	((id) >> 5)
+
+/* A full bank contains extra registers that we are not utilizing but still
+ * qualify as a single bank.
+ */
+#define SW_INIT_BANK_SIZE	0x18
+
+static inline
+struct brcmstb_reset *to_brcmstb(struct reset_controller_dev *rcdev)
+{
+	return container_of(rcdev, struct brcmstb_reset, rcdev);
+}
+
+static int brcmstb_reset_assert(struct reset_controller_dev *rcdev,
+				unsigned long id)
+{
+	unsigned int off = SW_INIT_BANK(id) * SW_INIT_BANK_SIZE;
+	struct brcmstb_reset *priv = to_brcmstb(rcdev);
+
+	writel_relaxed(SW_INIT_BIT(id), priv->base + off + SW_INIT_SET);
+
+	return 0;
+}
+
+static int brcmstb_reset_deassert(struct reset_controller_dev *rcdev,
+				  unsigned long id)
+{
+	unsigned int off = SW_INIT_BANK(id) * SW_INIT_BANK_SIZE;
+	struct brcmstb_reset *priv = to_brcmstb(rcdev);
+
+	writel_relaxed(SW_INIT_BIT(id), priv->base + off + SW_INIT_CLEAR);
+	/* Maximum reset delay after de-asserting a line and seeing block
+	 * operation is typically 14us for the worst case, build some slack
+	 * here.
+	 */
+	usleep_range(100, 200);
+
+	return 0;
+}
+
+static int brcmstb_reset_status(struct reset_controller_dev *rcdev,
+				unsigned long id)
+{
+	unsigned int off = SW_INIT_BANK(id) * SW_INIT_BANK_SIZE;
+	struct brcmstb_reset *priv = to_brcmstb(rcdev);
+
+	return readl_relaxed(priv->base + off + SW_INIT_STATUS) &
+			     SW_INIT_BIT(id);
+}
+
+static const struct reset_control_ops brcmstb_reset_ops = {
+	.assert	= brcmstb_reset_assert,
+	.deassert = brcmstb_reset_deassert,
+	.status = brcmstb_reset_status,
+};
+
+static int brcmstb_reset_probe(struct platform_device *pdev)
+{
+	struct device *kdev = &pdev->dev;
+	struct brcmstb_reset *priv;
+	struct resource *res;
+
+	priv = devm_kzalloc(kdev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	dev_set_drvdata(kdev, priv);
+
+	priv->rcdev.owner = THIS_MODULE;
+	priv->rcdev.nr_resets = DIV_ROUND_DOWN_ULL(resource_size(res),
+						   SW_INIT_BANK_SIZE) * 32;
+	priv->rcdev.ops = &brcmstb_reset_ops;
+	priv->rcdev.of_node = kdev->of_node;
+	/* Use defaults: 1 cell and simple xlate function */
+
+	return devm_reset_controller_register(kdev, &priv->rcdev);
+}
+
+static const struct of_device_id brcmstb_reset_of_match[] = {
+	{ .compatible = "brcm,brcmstb-reset" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, brcmstb_reset_of_match);
+
+static struct platform_driver brcmstb_reset_driver = {
+	.probe	= brcmstb_reset_probe,
+	.driver	= {
+		.name = "brcmstb-reset",
+		.of_match_table = brcmstb_reset_of_match,
+	},
+};
+module_platform_driver(brcmstb_reset_driver);
+
+MODULE_AUTHOR("Broadcom");
+MODULE_DESCRIPTION("Broadcom STB reset controller");
+MODULE_LICENSE("GPL");