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, 29 insertions, 0 deletions

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
new file mode 100644
index 000000000..b0e1423b0
--- /dev/null
+++ b/scripts/Makefile.gcc-plugins
@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: GPL-2.0
+
+gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
+gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)		\
+		+= -DLATENT_ENTROPY_PLUGIN
+ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
+    DISABLE_LATENT_ENTROPY_PLUGIN += -fplugin-arg-latent_entropy_plugin-disable -ULATENT_ENTROPY_PLUGIN
+endif
+export DISABLE_LATENT_ENTROPY_PLUGIN
+
+# All the plugin CFLAGS are collected here in case a build target needs to
+# filter them out of the KBUILD_CFLAGS.
+GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) -DGCC_PLUGINS
+export GCC_PLUGINS_CFLAGS
+
+# Add the flags to the build!
+KBUILD_CFLAGS += $(GCC_PLUGINS_CFLAGS)
+
+# Some plugins are enabled outside of this Makefile, but they still need to
+# be included in GCC_PLUGIN so they can get built.
+gcc-plugin-external-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)		\
+	+= randomize_layout_plugin.so
+gcc-plugin-external-$(CONFIG_GCC_PLUGIN_STACKLEAK)		\
+	+= stackleak_plugin.so
+
+# All enabled GCC plugins are collected here for building in
+# scripts/gcc-scripts/Makefile.
+GCC_PLUGIN := $(gcc-plugin-y) $(gcc-plugin-external-y)
+export GCC_PLUGIN