linux-kernel - [PATCH 5.0 162/238] powerpc/64s/hash: Fix assert_slb_presence() use of the slbfee. instruction

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Date:   Fri, 22 Mar 2019 12:16:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 5.0 162/238] powerpc/64s/hash: Fix assert_slb_presence() use of the slbfee. instruction

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

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

From: Nicholas Piggin <npiggin@...il.com>

commit 7104dccfd052fde51eecc9972dad9c40bd3e0d11 upstream.

The slbfee. instruction must have bit 24 of RB clear, failure to do
so can result in false negatives that result in incorrect assertions.

This is not obvious from the ISA v3.0B document, which only says:

    The hardware ignores the contents of RB 36:38 40:63 -- p.1032

This patch fixes the bug and also clears all other bits from PPC bit
36-63, which is good practice when dealing with reserved or ignored
bits.

Fixes: e15a4fea4dee ("powerpc/64s/hash: Add some SLB debugging tests")
Cc: stable@...r.kernel.org # v4.20+
Reported-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@...il.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/mm/slb.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -69,6 +69,11 @@ static void assert_slb_presence(bool pre
 	if (!cpu_has_feature(CPU_FTR_ARCH_206))
 		return;
 
+	/*
+	 * slbfee. requires bit 24 (PPC bit 39) be clear in RB. Hardware
+	 * ignores all other bits from 0-27, so just clear them all.
+	 */
+	ea &= ~((1UL << 28) - 1);
 	asm volatile(__PPC_SLBFEE_DOT(%0, %1) : "=r"(tmp) : "r"(ea) : "cr0");
 
 	WARN_ON(present == (tmp == 0));