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>

2 files changed, 38 insertions, 0 deletions

diff --git a/arch/arc/plat-sim/Makefile b/arch/arc/plat-sim/Makefile
new file mode 100644
index 000000000..ea9389bf8
--- /dev/null
+++ b/arch/arc/plat-sim/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2011-2012 Synopsys, Inc. (www.synopsys.com)
+#
+
+obj-y := platform.o
diff --git a/arch/arc/plat-sim/platform.c b/arch/arc/plat-sim/platform.c
new file mode 100644
index 000000000..2bde2a6e3
--- /dev/null
+++ b/arch/arc/plat-sim/platform.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ARC simulation Platform support code
+ *
+ * Copyright (C) 2012 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/init.h>
+#include <asm/mach_desc.h>
+
+/*----------------------- Machine Descriptions ------------------------------
+ *
+ * Machine description is simply a set of platform/board specific callbacks
+ * This is not directly related to DeviceTree based dynamic device creation,
+ * however as part of early device tree scan, we also select the right
+ * callback set, by matching the DT compatible name.
+ */
+
+static const char *simulation_compat[] __initconst = {
+#ifdef CONFIG_ISA_ARCOMPACT
+	"snps,nsim",
+	"snps,nsimosci",
+#else
+	"snps,nsimosci_hs",
+	"snps,zebu_hs",
+#endif
+	NULL,
+};
+
+MACHINE_START(SIMULATION, "simulation")
+	.dt_compat	= simulation_compat,
+MACHINE_END