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, 63 insertions, 0 deletions

diff --git a/drivers/misc/sram.h b/drivers/misc/sram.h
new file mode 100644
index 000000000..397205b8b
--- /dev/null
+++ b/drivers/misc/sram.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Defines for the SRAM driver
+ */
+#ifndef __SRAM_H
+#define __SRAM_H
+
+struct sram_config {
+	int (*init)(void);
+	bool map_only_reserved;
+};
+
+struct sram_partition {
+	void __iomem *base;
+
+	struct gen_pool *pool;
+	struct bin_attribute battr;
+	struct mutex lock;
+	struct list_head list;
+};
+
+struct sram_dev {
+	const struct sram_config *config;
+
+	struct device *dev;
+	void __iomem *virt_base;
+	bool no_memory_wc;
+
+	struct gen_pool *pool;
+
+	struct sram_partition *partition;
+	u32 partitions;
+};
+
+struct sram_reserve {
+	struct list_head list;
+	u32 start;
+	u32 size;
+	struct resource res;
+	bool export;
+	bool pool;
+	bool protect_exec;
+	const char *label;
+};
+
+#ifdef CONFIG_SRAM_EXEC
+int sram_check_protect_exec(struct sram_dev *sram, struct sram_reserve *block,
+			    struct sram_partition *part);
+int sram_add_protect_exec(struct sram_partition *part);
+#else
+static inline int sram_check_protect_exec(struct sram_dev *sram,
+					  struct sram_reserve *block,
+					  struct sram_partition *part)
+{
+	return -ENODEV;
+}
+
+static inline int sram_add_protect_exec(struct sram_partition *part)
+{
+	return -ENODEV;
+}
+#endif /* CONFIG_SRAM_EXEC */
+#endif /* __SRAM_H */