From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Joe Mario , Jiri Kosina , Josh Poimboeuf , Peter Zijlstra , David Woodhouse Subject: [PATCH 4.9 082/107] cpu/hotplug: detect SMT disabled by BIOS Date: Tue, 14 Aug 2018 19:17:45 +0200 Message-Id: <20180814171525.784747037@linuxfoundation.org> In-Reply-To: <20180814171520.883143803@linuxfoundation.org> References: <20180814171520.883143803@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josh Poimboeuf commit 73d5e2b472640b1fcdb61ae8be389912ef211bda upstream If SMT is disabled in BIOS, the CPU code doesn't properly detect it. The /sys/devices/system/cpu/smt/control file shows 'on', and the 'l1tf' vulnerabilities file shows SMT as vulnerable. Fix it by forcing 'cpu_smt_control' to CPU_SMT_NOT_SUPPORTED in such a case. Unfortunately the detection can only be done after bringing all the CPUs online, so we have to overwrite any previous writes to the variable. Reported-by: Joe Mario Tested-by: Jiri Kosina Fixes: f048c399e0f7 ("x86/topology: Provide topology_smt_supported()") Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra Signed-off-by: David Woodhouse Signed-off-by: Greg Kroah-Hartman --- kernel/cpu.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2063,6 +2063,15 @@ static const struct attribute_group cpuh static int __init cpu_smt_state_init(void) { + /* + * If SMT was disabled by BIOS, detect it here, after the CPUs have + * been brought online. This ensures the smt/l1tf sysfs entries are + * consistent with reality. Note this may overwrite cpu_smt_control's + * previous setting. + */ + if (topology_max_smt_threads() == 1) + cpu_smt_control = CPU_SMT_NOT_SUPPORTED; + return sysfs_create_group(&cpu_subsys.dev_root->kobj, &cpuhp_smt_attr_group); }