powerpc/64s/radix: Fix radix_kvm_prefetch_workaround paca access of not possible CPU

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@kernel.org
Reported-by: Pridhiviraj Paidipeddi <ppaidipe@linux.vnet.ibm.com>
Tested-by: Pridhiviraj Paidipeddi <ppaidipe@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c
index a5d7309c2d0555996dc44bfa52430e3484927eff..465cb604b33a0e0aa05fd878866f90ba7c26c396 100644 (file)
--- a/arch/powerpc/mm/tlb-radix.c
+++ b/arch/powerpc/mm/tlb-radix.c
@@ -733,6 +733,8 @@ extern void radix_kvm_prefetch_workaround(struct mm_struct *mm)
                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;
                }