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, 74 insertions, 0 deletions

diff --git a/lib/crypto/mpi/mpi-cmp.c b/lib/crypto/mpi/mpi-cmp.c
new file mode 100644
index 000000000..b42929296
--- /dev/null
+++ b/lib/crypto/mpi/mpi-cmp.c
@@ -0,0 +1,74 @@
+/* mpi-cmp.c  -  MPI functions
+ * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include <linux/export.h>
+
+#include "mpi-internal.h"
+
+int mpi_cmp_ui(MPI u, unsigned long v)
+{
+	mpi_limb_t limb = v;
+
+	mpi_normalize(u);
+	if (u->nlimbs == 0) {
+		if (v == 0)
+			return 0;
+		else
+			return -1;
+	}
+	if (u->sign)
+		return -1;
+	if (u->nlimbs > 1)
+		return 1;
+
+	if (u->d[0] == limb)
+		return 0;
+	else if (u->d[0] > limb)
+		return 1;
+	else
+		return -1;
+}
+EXPORT_SYMBOL_GPL(mpi_cmp_ui);
+
+int mpi_cmp(MPI u, MPI v)
+{
+	mpi_size_t usize, vsize;
+	int cmp;
+
+	mpi_normalize(u);
+	mpi_normalize(v);
+	usize = u->nlimbs;
+	vsize = v->nlimbs;
+	if (!u->sign && v->sign)
+		return 1;
+	if (u->sign && !v->sign)
+		return -1;
+	if (usize != vsize && !u->sign && !v->sign)
+		return usize - vsize;
+	if (usize != vsize && u->sign && v->sign)
+		return vsize - usize;
+	if (!usize)
+		return 0;
+	cmp = mpihelp_cmp(u->d, v->d, usize);
+	if (u->sign)
+		return -cmp;
+	return cmp;
+}
+EXPORT_SYMBOL_GPL(mpi_cmp);