linux-kernel - [PATCH 4.9 043/125] powerpc/mm/radix: Properly clear process table entry

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Date:   Tue, 25 Jul 2017 12:19:18 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.9 043/125] powerpc/mm/radix: Properly clear process table entry

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

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

From: Benjamin Herrenschmidt <benh@...nel.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@...nel.crashing.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -167,9 +167,15 @@ 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);