Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753997AbcDZUcP (ORCPT ); Tue, 26 Apr 2016 16:32:15 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:58388 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753699AbcDZUZ6 (ORCPT ); Tue, 26 Apr 2016 16:25:58 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Anton Blanchard , Michael Ellerman , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 42/66] powerpc: scan_features() updates incorrect bits for REAL_LE Date: Tue, 26 Apr 2016 13:24:33 -0700 Message-Id: <1461702297-7792-43-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1461702297-7792-1-git-send-email-kamal@canonical.com> References: <1461702297-7792-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3280 Lines: 83 3.19.8-ckt20 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Anton Blanchard commit 6997e57d693b07289694239e52a10d2f02c3a46f upstream. The REAL_LE feature entry in the ibm_pa_feature struct is missing an MMU feature value, meaning all the remaining elements initialise the wrong values. This means instead of checking for byte 5, bit 0, we check for byte 0, bit 0, and then we incorrectly set the CPU feature bit as well as MMU feature bit 1 and CPU user feature bits 0 and 2 (5). Checking byte 0 bit 0 (IBM numbering), means we're looking at the "Memory Management Unit (MMU)" feature - ie. does the CPU have an MMU. In practice that bit is set on all platforms which have the property. This means we set CPU_FTR_REAL_LE always. In practice that seems not to matter because all the modern cpus which have this property also implement REAL_LE, and we've never needed to disable it. We're also incorrectly setting MMU feature bit 1, which is: #define MMU_FTR_TYPE_8xx 0x00000002 Luckily the only place that looks for MMU_FTR_TYPE_8xx is in Book3E code, which can't run on the same cpus as scan_features(). So this also doesn't matter in practice. Finally in the CPU user feature mask, we're setting bits 0 and 2. Bit 2 is not currently used, and bit 0 is: #define PPC_FEATURE_PPC_LE 0x00000001 Which says the CPU supports the old style "PPC Little Endian" mode. Again this should be harmless in practice as no 64-bit CPUs implement that mode. Fix the code by adding the missing initialisation of the MMU feature. Also add a comment marking CPU user feature bit 2 (0x4) as reserved. It would be unsafe to start using it as old kernels incorrectly set it. Fixes: 44ae3ab3358e ("powerpc: Free up some CPU feature bits by moving out MMU-related features") Signed-off-by: Anton Blanchard [mpe: Flesh out changelog, add comment reserving 0x4] Signed-off-by: Michael Ellerman Signed-off-by: Kamal Mostafa --- arch/powerpc/include/uapi/asm/cputable.h | 1 + arch/powerpc/kernel/prom.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/uapi/asm/cputable.h b/arch/powerpc/include/uapi/asm/cputable.h index de2c0e4..67de80a 100644 --- a/arch/powerpc/include/uapi/asm/cputable.h +++ b/arch/powerpc/include/uapi/asm/cputable.h @@ -31,6 +31,7 @@ #define PPC_FEATURE_PSERIES_PERFMON_COMPAT \ 0x00000040 +/* Reserved - do not use 0x00000004 */ #define PPC_FEATURE_TRUE_LE 0x00000002 #define PPC_FEATURE_PPC_LE 0x00000001 diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c index 6a799b3..149a504 100644 --- a/arch/powerpc/kernel/prom.c +++ b/arch/powerpc/kernel/prom.c @@ -159,7 +159,7 @@ static struct ibm_pa_feature { {CPU_FTR_NOEXECUTE, 0, 0, 0, 6, 0}, {CPU_FTR_NODSISRALIGN, 0, 0, 1, 1, 1}, {0, MMU_FTR_CI_LARGE_PAGE, 0, 1, 2, 0}, - {CPU_FTR_REAL_LE, PPC_FEATURE_TRUE_LE, 5, 0, 0}, + {CPU_FTR_REAL_LE, 0, PPC_FEATURE_TRUE_LE, 5, 0, 0}, /* * If the kernel doesn't support TM (ie. CONFIG_PPC_TRANSACTIONAL_MEM=n), * we don't want to turn on CPU_FTR_TM here, so we use CPU_FTR_TM_COMP -- 2.7.4