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, 40 insertions, 0 deletions

diff --git a/include/crypto/internal/simd.h b/include/crypto/internal/simd.h
new file mode 100644
index 000000000..f5e5d7b63
--- /dev/null
+++ b/include/crypto/internal/simd.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Shared crypto simd helpers
+ */
+
+#ifndef _CRYPTO_INTERNAL_SIMD_H
+#define _CRYPTO_INTERNAL_SIMD_H
+
+#include <asm/simd.h>
+#include <linux/percpu.h>
+#include <linux/types.h>
+
+struct simd_aead_alg;
+struct aead_alg;
+
+int simd_register_aeads_compat(struct aead_alg *algs, int count,
+			       struct simd_aead_alg **simd_algs);
+
+void simd_unregister_aeads(struct aead_alg *algs, int count,
+			   struct simd_aead_alg **simd_algs);
+
+/*
+ * crypto_simd_usable() - is it allowed at this time to use SIMD instructions or
+ *			  access the SIMD register file?
+ *
+ * This delegates to may_use_simd(), except that this also returns false if SIMD
+ * in crypto code has been temporarily disabled on this CPU by the crypto
+ * self-tests, in order to test the no-SIMD fallback code.  This override is
+ * currently limited to configurations where the "full" self-tests are enabled,
+ * because it might be a bit too invasive to be part of the "fast" self-tests.
+ */
+#ifdef CONFIG_CRYPTO_SELFTESTS_FULL
+DECLARE_PER_CPU(bool, crypto_simd_disabled_for_test);
+#define crypto_simd_usable() \
+	(may_use_simd() && !this_cpu_read(crypto_simd_disabled_for_test))
+#else
+#define crypto_simd_usable() may_use_simd()
+#endif
+
+#endif /* _CRYPTO_INTERNAL_SIMD_H */