[PATCH 4.17 056/220] powerpc/64s/radix: Fix radix_kvm_prefetch_workaround paca access of not possible CPU

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Piggin <npiggin@xxxxxxxxx>

commit 758380b8155f69b4e2f77f27562f8a7a466749d6 upstream.

If possible CPUs are limited (e.g., by kexec), then the kvm prefetch
workaround function can access the paca pointer for a !possible CPU.

Fixes: d2e60075a3d44 ("powerpc/64: Use array of paca pointers and allocate pacas individually")
Cc: stable@xxxxxxxxxx
Reported-by: Pridhiviraj Paidipeddi <ppaidipe@xxxxxxxxxxxxxxxxxx>
Tested-by: Pridhiviraj Paidipeddi <ppaidipe@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/powerpc/mm/tlb-radix.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/powerpc/mm/tlb-radix.c
+++ b/arch/powerpc/mm/tlb-radix.c
@@ -733,6 +733,8 @@ extern void radix_kvm_prefetch_workaroun
 		for (; sib <= cpu_last_thread_sibling(cpu) && !flush; sib++) {
 			if (sib == cpu)
 				continue;
+			if (!cpu_possible(sib))
+				continue;
 			if (paca_ptrs[sib]->kvm_hstate.kvm_vcpu)
 				flush = true;
 		}