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, 120 insertions, 0 deletions

diff --git a/drivers/reset/reset-socfpga.c b/drivers/reset/reset-socfpga.c
new file mode 100644
index 000000000..da208270b
--- /dev/null
+++ b/drivers/reset/reset-socfpga.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018, Intel Corporation
+ * Copied from reset-sunxi.c
+ */
+
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+#include <linux/reset/reset-simple.h>
+#include <linux/reset/socfpga.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+
+#define SOCFPGA_NR_BANKS	8
+
+static int a10_reset_init(struct device_node *np)
+{
+	struct reset_simple_data *data;
+	struct resource res;
+	resource_size_t size;
+	int ret;
+	u32 reg_offset = 0x10;
+
+	data = kzalloc_obj(*data);
+	if (!data)
+		return -ENOMEM;
+
+	ret = of_address_to_resource(np, 0, &res);
+	if (ret)
+		goto err_alloc;
+
+	size = resource_size(&res);
+	if (!request_mem_region(res.start, size, np->name)) {
+		ret = -EBUSY;
+		goto err_alloc;
+	}
+
+	data->membase = ioremap(res.start, size);
+	if (!data->membase) {
+		ret = -ENOMEM;
+		goto release_region;
+	}
+
+	if (of_property_read_u32(np, "altr,modrst-offset", &reg_offset))
+		pr_warn("missing altr,modrst-offset property, assuming 0x10\n");
+	data->membase += reg_offset;
+
+	spin_lock_init(&data->lock);
+
+	data->rcdev.owner = THIS_MODULE;
+	data->rcdev.nr_resets = SOCFPGA_NR_BANKS * 32;
+	data->rcdev.ops = &reset_simple_ops;
+	data->rcdev.of_node = np;
+	data->status_active_low = true;
+
+	ret = reset_controller_register(&data->rcdev);
+	if (ret)
+		pr_err("unable to register device\n");
+
+	return ret;
+
+release_region:
+	release_mem_region(res.start, size);
+
+err_alloc:
+	kfree(data);
+	return ret;
+};
+
+/*
+ * These are the reset controller we need to initialize early on in
+ * our system, before we can even think of using a regular device
+ * driver for it.
+ * The controllers that we can register through the regular device
+ * model are handled by the simple reset driver directly.
+ */
+static const struct of_device_id socfpga_early_reset_dt_ids[] __initconst = {
+	{ .compatible = "altr,rst-mgr", },
+	{ /* sentinel */ },
+};
+
+void __init socfpga_reset_init(void)
+{
+	struct device_node *np;
+
+	for_each_matching_node(np, socfpga_early_reset_dt_ids)
+		a10_reset_init(np);
+}
+
+/*
+ * The early driver is problematic, because it doesn't register
+ * itself as a driver. This causes certain device links to prevent
+ * consumer devices from probing. The hacky solution is to register
+ * an empty driver, whose only job is to attach itself to the reset
+ * manager and call probe.
+ */
+static const struct of_device_id socfpga_reset_dt_ids[] = {
+	{ .compatible = "altr,rst-mgr", },
+	{ /* sentinel */ },
+};
+
+static int reset_simple_probe(struct platform_device *pdev)
+{
+	return 0;
+}
+
+static struct platform_driver reset_socfpga_driver = {
+	.probe	= reset_simple_probe,
+	.driver = {
+		.name		= "socfpga-reset",
+		.of_match_table	= socfpga_reset_dt_ids,
+	},
+};
+builtin_platform_driver(reset_socfpga_driver);