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, 107 insertions, 0 deletions

diff --git a/drivers/nvmem/meson-efuse.c b/drivers/nvmem/meson-efuse.c
new file mode 100644
index 000000000..d7f9ac99a
--- /dev/null
+++ b/drivers/nvmem/meson-efuse.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Amlogic Meson GX eFuse Driver
+ *
+ * Copyright (c) 2016 Endless Computers, Inc.
+ * Author: Carlo Caione <carlo@endlessm.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+#include <linux/firmware/meson/meson_sm.h>
+
+static int meson_efuse_read(void *context, unsigned int offset,
+			    void *val, size_t bytes)
+{
+	struct meson_sm_firmware *fw = context;
+	int ret;
+
+	ret = meson_sm_call_read(fw, (u8 *)val, bytes, SM_EFUSE_READ, offset,
+				 bytes, 0, 0, 0);
+
+	return ret < 0 ? ret : 0;
+}
+
+static int meson_efuse_write(void *context, unsigned int offset,
+			     void *val, size_t bytes)
+{
+	struct meson_sm_firmware *fw = context;
+	int ret;
+
+	ret = meson_sm_call_write(fw, (u8 *)val, bytes, SM_EFUSE_WRITE, offset,
+				  bytes, 0, 0, 0);
+
+	return ret < 0 ? ret : 0;
+}
+
+static const struct of_device_id meson_efuse_match[] = {
+	{ .compatible = "amlogic,meson-gxbb-efuse", },
+	{ /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, meson_efuse_match);
+
+static int meson_efuse_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct meson_sm_firmware *fw;
+	struct nvmem_device *nvmem;
+	struct nvmem_config *econfig;
+	struct clk *clk;
+	unsigned int size;
+	struct device_node *sm_np __free(device_node) =
+			of_parse_phandle(pdev->dev.of_node, "secure-monitor", 0);
+
+	if (!sm_np) {
+		dev_err(&pdev->dev, "no secure-monitor node\n");
+		return -ENODEV;
+	}
+
+	fw = meson_sm_get(sm_np);
+	if (!fw)
+		return -EPROBE_DEFER;
+
+	clk = devm_clk_get_enabled(dev, NULL);
+	if (IS_ERR(clk))
+		return dev_err_probe(dev, PTR_ERR(clk), "failed to get efuse gate");
+
+	if (meson_sm_call(fw, SM_EFUSE_USER_MAX, &size, 0, 0, 0, 0, 0) < 0) {
+		dev_err(dev, "failed to get max user");
+		return -EINVAL;
+	}
+
+	econfig = devm_kzalloc(dev, sizeof(*econfig), GFP_KERNEL);
+	if (!econfig)
+		return -ENOMEM;
+
+	econfig->dev = dev;
+	econfig->name = dev_name(dev);
+	econfig->add_legacy_fixed_of_cells = true;
+	econfig->stride = 1;
+	econfig->word_size = 1;
+	econfig->reg_read = meson_efuse_read;
+	econfig->reg_write = meson_efuse_write;
+	econfig->size = size;
+	econfig->priv = fw;
+
+	nvmem = devm_nvmem_register(&pdev->dev, econfig);
+
+	return PTR_ERR_OR_ZERO(nvmem);
+}
+
+static struct platform_driver meson_efuse_driver = {
+	.probe = meson_efuse_probe,
+	.driver = {
+		.name = "meson-efuse",
+		.of_match_table = meson_efuse_match,
+	},
+};
+
+module_platform_driver(meson_efuse_driver);
+
+MODULE_AUTHOR("Carlo Caione <carlo@endlessm.com>");
+MODULE_DESCRIPTION("Amlogic Meson GX NVMEM driver");
+MODULE_LICENSE("GPL v2");