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, 81 insertions, 0 deletions

diff --git a/drivers/nvmem/apple-efuses.c b/drivers/nvmem/apple-efuses.c
new file mode 100644
index 000000000..9913e77b8
--- /dev/null
+++ b/drivers/nvmem/apple-efuses.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Apple SoC eFuse driver
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+
+struct apple_efuses_priv {
+	void __iomem *fuses;
+};
+
+static int apple_efuses_read(void *context, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct apple_efuses_priv *priv = context;
+	u32 *dst = val;
+
+	while (bytes >= sizeof(u32)) {
+		*dst++ = readl_relaxed(priv->fuses + offset);
+		bytes -= sizeof(u32);
+		offset += sizeof(u32);
+	}
+
+	return 0;
+}
+
+static int apple_efuses_probe(struct platform_device *pdev)
+{
+	struct apple_efuses_priv *priv;
+	struct resource *res;
+	struct nvmem_config config = {
+		.dev = &pdev->dev,
+		.add_legacy_fixed_of_cells = true,
+		.read_only = true,
+		.reg_read = apple_efuses_read,
+		.stride = sizeof(u32),
+		.word_size = sizeof(u32),
+		.name = "apple_efuses_nvmem",
+		.id = NVMEM_DEVID_AUTO,
+		.root_only = true,
+	};
+
+	priv = devm_kzalloc(config.dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->fuses = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(priv->fuses))
+		return PTR_ERR(priv->fuses);
+
+	config.priv = priv;
+	config.size = resource_size(res);
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(config.dev, &config));
+}
+
+static const struct of_device_id apple_efuses_of_match[] = {
+	{ .compatible = "apple,efuses", },
+	{}
+};
+
+MODULE_DEVICE_TABLE(of, apple_efuses_of_match);
+
+static struct platform_driver apple_efuses_driver = {
+	.driver = {
+		.name = "apple_efuses",
+		.of_match_table = apple_efuses_of_match,
+	},
+	.probe = apple_efuses_probe,
+};
+
+module_platform_driver(apple_efuses_driver);
+
+MODULE_AUTHOR("Sven Peter <sven@svenpeter.dev>");
+MODULE_DESCRIPTION("Apple SoC eFuse driver");
+MODULE_LICENSE("GPL");