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/arch/xtensa/lib/ashrdi3.S b/arch/xtensa/lib/ashrdi3.S
new file mode 100644
index 000000000..07bc6e758
--- /dev/null
+++ b/arch/xtensa/lib/ashrdi3.S
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later WITH GCC-exception-2.0 */
+#include <linux/linkage.h>
+#include <asm/asmmacro.h>
+#include <asm/core.h>
+
+#ifdef __XTENSA_EB__
+#define uh a2
+#define ul a3
+#else
+#define uh a3
+#define ul a2
+#endif /* __XTENSA_EB__ */
+
+ENTRY(__ashrdi3)
+
+	abi_entry_default
+	ssr	a4
+	bgei	a4, 32, .Lhigh_only
+	src	ul, uh, ul
+	sra	uh, uh
+	abi_ret_default
+
+.Lhigh_only:
+	sra	ul, uh
+	srai	uh, uh, 31
+	abi_ret_default
+
+ENDPROC(__ashrdi3)
+EXPORT_SYMBOL(__ashrdi3)