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, 80 insertions, 0 deletions

diff --git a/drivers/soc/apple/tunable.c b/drivers/soc/apple/tunable.c
new file mode 100644
index 000000000..659323839
--- /dev/null
+++ b/drivers/soc/apple/tunable.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple Silicon hardware tunable support
+ *
+ * Each tunable is a list with each entry containing a offset into the MMIO
+ * region, a mask of bits to be cleared and a set of bits to be set. These
+ * tunables are passed along by the previous boot stages and vary from device
+ * to device such that they cannot be hardcoded in the individual drivers.
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/overflow.h>
+#include <linux/soc/apple/tunable.h>
+
+struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
+					       struct device_node *np,
+					       const char *name,
+					       struct resource *res)
+{
+	struct apple_tunable *tunable;
+	struct property *prop;
+	const __be32 *p;
+	size_t sz;
+	int i;
+
+	if (resource_size(res) < 4)
+		return ERR_PTR(-EINVAL);
+
+	prop = of_find_property(np, name, NULL);
+	if (!prop)
+		return ERR_PTR(-ENOENT);
+
+	if (prop->length % (3 * sizeof(u32)))
+		return ERR_PTR(-EINVAL);
+	sz = prop->length / (3 * sizeof(u32));
+
+	tunable = devm_kzalloc(dev, struct_size(tunable, values, sz), GFP_KERNEL);
+	if (!tunable)
+		return ERR_PTR(-ENOMEM);
+	tunable->sz = sz;
+
+	for (i = 0, p = NULL; i < tunable->sz; ++i) {
+		p = of_prop_next_u32(prop, p, &tunable->values[i].offset);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].mask);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].value);
+
+		/* Sanity checks to catch bugs in our bootloader */
+		if (tunable->values[i].offset % 4)
+			return ERR_PTR(-EINVAL);
+		if (tunable->values[i].offset > (resource_size(res) - 4))
+			return ERR_PTR(-EINVAL);
+	}
+
+	return tunable;
+}
+EXPORT_SYMBOL(devm_apple_tunable_parse);
+
+void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable)
+{
+	size_t i;
+
+	for (i = 0; i < tunable->sz; ++i) {
+		u32 val, old_val;
+
+		old_val = readl(regs + tunable->values[i].offset);
+		val = old_val & ~tunable->values[i].mask;
+		val |= tunable->values[i].value;
+		if (val != old_val)
+			writel(val, regs + tunable->values[i].offset);
+	}
+}
+EXPORT_SYMBOL(apple_tunable_apply);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_AUTHOR("Sven Peter <sven@kernel.org>");
+MODULE_DESCRIPTION("Apple Silicon hardware tunable support");