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, 26 insertions, 0 deletions

diff --git a/arch/powerpc/boot/reg.h b/arch/powerpc/boot/reg.h
new file mode 100644
index 000000000..fd8f4fcbf
--- /dev/null
+++ b/arch/powerpc/boot/reg.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _PPC_BOOT_REG_H
+#define _PPC_BOOT_REG_H
+/*
+ * Copyright 2007 Davud Gibson, IBM Corporation.
+ */
+
+static inline u32 mfpvr(void)
+{
+	u32 pvr;
+	asm volatile ("mfpvr	%0" : "=r"(pvr));
+	return pvr;
+}
+
+#define __stringify_1(x)	#x
+#define __stringify(x)		__stringify_1(x)
+
+#define mfspr(rn)	({unsigned long rval; \
+			asm volatile("mfspr %0," __stringify(rn) \
+				: "=r" (rval)); rval; })
+#define mtspr(rn, v)	asm volatile("mtspr " __stringify(rn) ",%0" : : "r" (v))
+
+register void *__stack_pointer asm("r1");
+#define get_sp()	(__stack_pointer)
+
+#endif	/* _PPC_BOOT_REG_H */