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, 125 insertions, 0 deletions

diff --git a/include/drm/drm_module.h b/include/drm/drm_module.h
new file mode 100644
index 000000000..4db1ae03d
--- /dev/null
+++ b/include/drm/drm_module.h
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: MIT */
+
+#ifndef DRM_MODULE_H
+#define DRM_MODULE_H
+
+#include <linux/pci.h>
+#include <linux/platform_device.h>
+
+#include <drm/drm_drv.h>
+
+/**
+ * DOC: overview
+ *
+ * This library provides helpers registering DRM drivers during module
+ * initialization and shutdown. The provided helpers act like bus-specific
+ * module helpers, such as module_pci_driver(), but respect additional
+ * parameters that control DRM driver registration.
+ *
+ * Below is an example of initializing a DRM driver for a device on the
+ * PCI bus.
+ *
+ * .. code-block:: c
+ *
+ *	struct pci_driver my_pci_drv = {
+ *	};
+ *
+ *	drm_module_pci_driver(my_pci_drv);
+ *
+ * The generated code will test if DRM drivers are enabled and register
+ * the PCI driver my_pci_drv. For more complex module initialization, you
+ * can still use module_init() and module_exit() in your driver.
+ */
+
+/*
+ * PCI drivers
+ */
+
+static inline int __init drm_pci_register_driver(struct pci_driver *pci_drv)
+{
+	if (drm_firmware_drivers_only())
+		return -ENODEV;
+
+	return pci_register_driver(pci_drv);
+}
+
+/**
+ * drm_module_pci_driver - Register a DRM driver for PCI-based devices
+ * @__pci_drv: the PCI driver structure
+ *
+ * Registers a DRM driver for devices on the PCI bus. The helper
+ * macro behaves like module_pci_driver() but tests the state of
+ * drm_firmware_drivers_only(). For more complex module initialization,
+ * use module_init() and module_exit() directly.
+ *
+ * Each module may only use this macro once. Calling it replaces
+ * module_init() and module_exit().
+ */
+#define drm_module_pci_driver(__pci_drv) \
+	module_driver(__pci_drv, drm_pci_register_driver, pci_unregister_driver)
+
+static inline int __init
+drm_pci_register_driver_if_modeset(struct pci_driver *pci_drv, int modeset)
+{
+	if (drm_firmware_drivers_only() && modeset == -1)
+		return -ENODEV;
+	if (modeset == 0)
+		return -ENODEV;
+
+	return pci_register_driver(pci_drv);
+}
+
+static inline void __exit
+drm_pci_unregister_driver_if_modeset(struct pci_driver *pci_drv, int modeset)
+{
+	pci_unregister_driver(pci_drv);
+}
+
+/**
+ * drm_module_pci_driver_if_modeset - Register a DRM driver for PCI-based devices
+ * @__pci_drv: the PCI driver structure
+ * @__modeset: an additional parameter that disables the driver
+ *
+ * This macro is deprecated and only provided for existing drivers. For
+ * new drivers, use drm_module_pci_driver().
+ *
+ * Registers a DRM driver for devices on the PCI bus. The helper macro
+ * behaves like drm_module_pci_driver() with an additional driver-specific
+ * flag. If __modeset is 0, the driver has been disabled, if __modeset is
+ * -1 the driver state depends on the global DRM state. For all other
+ * values, the PCI driver has been enabled. The default should be -1.
+ */
+#define drm_module_pci_driver_if_modeset(__pci_drv, __modeset) \
+	module_driver(__pci_drv, drm_pci_register_driver_if_modeset, \
+		      drm_pci_unregister_driver_if_modeset, __modeset)
+
+/*
+ * Platform drivers
+ */
+
+static inline int __init
+drm_platform_driver_register(struct platform_driver *platform_drv)
+{
+	if (drm_firmware_drivers_only())
+		return -ENODEV;
+
+	return platform_driver_register(platform_drv);
+}
+
+/**
+ * drm_module_platform_driver - Register a DRM driver for platform devices
+ * @__platform_drv: the platform driver structure
+ *
+ * Registers a DRM driver for devices on the platform bus. The helper
+ * macro behaves like module_platform_driver() but tests the state of
+ * drm_firmware_drivers_only(). For more complex module initialization,
+ * use module_init() and module_exit() directly.
+ *
+ * Each module may only use this macro once. Calling it replaces
+ * module_init() and module_exit().
+ */
+#define drm_module_platform_driver(__platform_drv) \
+	module_driver(__platform_drv, drm_platform_driver_register, \
+		      platform_driver_unregister)
+
+#endif