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, 20 insertions, 0 deletions

diff --git a/include/asm-generic/bitops/non-atomic.h b/include/asm-generic/bitops/non-atomic.h
new file mode 100644
index 000000000..71f8d54a5
--- /dev/null
+++ b/include/asm-generic/bitops/non-atomic.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_BITOPS_NON_ATOMIC_H_
+#define _ASM_GENERIC_BITOPS_NON_ATOMIC_H_
+
+#include <asm-generic/bitops/generic-non-atomic.h>
+
+#define arch___set_bit generic___set_bit
+#define arch___clear_bit generic___clear_bit
+#define arch___change_bit generic___change_bit
+
+#define arch___test_and_set_bit generic___test_and_set_bit
+#define arch___test_and_clear_bit generic___test_and_clear_bit
+#define arch___test_and_change_bit generic___test_and_change_bit
+
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
+
+#include <asm-generic/bitops/non-instrumented-non-atomic.h>
+
+#endif /* _ASM_GENERIC_BITOPS_NON_ATOMIC_H_ */