powerpc/mm/radix: Properly clear process table entry

On radix, the process table entry we want to clear when destroying a
context is entry 0, not entry 1. This has no *immediate* consequence
on Power9, but it can cause other bugs to become worse.

Fixes: 7e381c0ff618 ("powerpc/mm/radix: Add mmu context handling callback for radix")
Cc: stable@vger.kernel.org # v4.7+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index 71de2c6d88f34bfaafe4d759154f102cdc088045..ceff76262c7e8429f93719a3a3e7552c4e3e3c4e 100644 (file)
--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -223,9 +223,15 @@ void destroy_context(struct mm_struct *mm)
        mm->context.cop_lockp = NULL;
 #endif /* CONFIG_PPC_ICSWX */
 
-       if (radix_enabled())
-               process_tb[mm->context.id].prtb1 = 0;
-       else
+       if (radix_enabled()) {
+               /*
+                * Radix doesn't have a valid bit in the process table
+                * entries. However we know that at least P9 implementation
+                * will avoid caching an entry with an invalid RTS field,
+                * and 0 is invalid. So this will do.
+                */
+               process_tb[mm->context.id].prtb0 = 0;
+       } else
                subpage_prot_free(mm);
        destroy_pagetable_page(mm);
        __destroy_context(mm->context.id);