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Subject[PATCH 4.12 056/196] powerpc/mm/radix: Properly clear process table entry
Date
4.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

commit c6bb0b8d426a8cf865ca9c8a532cc3a2927cfceb upstream.

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")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/mm/mmu_context_book3s64.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

--- 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 *m
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);

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