arch/x86/kernel/cpu/tsx.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Intel Transactional Synchronization Extensions (TSX) control.
   4  *
   5  * Copyright (C) 2019 Intel Corporation
   6  *
   7  * Author:
   8  *      Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
   9  */
  10
  11 #include <linux/cpufeature.h>
  12
  13 #include <asm/cmdline.h>
  14
  15 #include "cpu.h"
  16
  17 enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
  18
  19 void tsx_disable(void)
  20 {
  21         u64 tsx;
  22
  23         rdmsrl(MSR_IA32_TSX_CTRL, tsx);
  24
  25         /* Force all transactions to immediately abort */
  26         tsx |= TSX_CTRL_RTM_DISABLE;
  27
  28         /*
  29          * Ensure TSX support is not enumerated in CPUID.
  30          * This is visible to userspace and will ensure they
  31          * do not waste resources trying TSX transactions that
  32          * will always abort.
  33          */
  34         tsx |= TSX_CTRL_CPUID_CLEAR;
  35
  36         wrmsrl(MSR_IA32_TSX_CTRL, tsx);
  37 }
  38
  39 void tsx_enable(void)
  40 {
  41         u64 tsx;
  42
  43         rdmsrl(MSR_IA32_TSX_CTRL, tsx);
  44
  45         /* Enable the RTM feature in the cpu */
  46         tsx &= ~TSX_CTRL_RTM_DISABLE;
  47
  48         /*
  49          * Ensure TSX support is enumerated in CPUID.
  50          * This is visible to userspace and will ensure they
  51          * can enumerate and use the TSX feature.
  52          */
  53         tsx &= ~TSX_CTRL_CPUID_CLEAR;
  54
  55         wrmsrl(MSR_IA32_TSX_CTRL, tsx);
  56 }
  57
  58 static bool __init tsx_ctrl_is_supported(void)
  59 {
  60         u64 ia32_cap = x86_read_arch_cap_msr();
  61
  62         /*
  63          * TSX is controlled via MSR_IA32_TSX_CTRL.  However, support for this
  64          * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
  65          *
  66          * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
  67          * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
  68          * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
  69          * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
  70          * tsx= cmdline requests will do nothing on CPUs without
  71          * MSR_IA32_TSX_CTRL support.
  72          */
  73         return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
  74 }
  75
  76 static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
  77 {
  78         if (boot_cpu_has_bug(X86_BUG_TAA))
  79                 return TSX_CTRL_DISABLE;
  80
  81         return TSX_CTRL_ENABLE;
  82 }
  83
  84 void __init tsx_init(void)
  85 {
  86         char arg[5] = {};
  87         int ret;
  88
  89         if (!tsx_ctrl_is_supported())
  90                 return;
  91
  92         ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
  93         if (ret >= 0) {
  94                 if (!strcmp(arg, "on")) {
  95                         tsx_ctrl_state = TSX_CTRL_ENABLE;
  96                 } else if (!strcmp(arg, "off")) {
  97                         tsx_ctrl_state = TSX_CTRL_DISABLE;
  98                 } else if (!strcmp(arg, "auto")) {
  99                         tsx_ctrl_state = x86_get_tsx_auto_mode();
 100                 } else {
 101                         tsx_ctrl_state = TSX_CTRL_DISABLE;
 102                         pr_err("tsx: invalid option, defaulting to off\n");
 103                 }
 104         } else {
 105                 /* tsx= not provided */
 106                 if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
 107                         tsx_ctrl_state = x86_get_tsx_auto_mode();
 108                 else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
 109                         tsx_ctrl_state = TSX_CTRL_DISABLE;
 110                 else
 111                         tsx_ctrl_state = TSX_CTRL_ENABLE;
 112         }
 113
 114         if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
 115                 tsx_disable();
 116
 117                 /*
 118                  * tsx_disable() will change the state of the
 119                  * RTM CPUID bit.  Clear it here since it is now
 120                  * expected to be not set.
 121                  */
 122                 setup_clear_cpu_cap(X86_FEATURE_RTM);
 123         } else if (tsx_ctrl_state == TSX_CTRL_ENABLE) {
 124
 125                 /*
 126                  * HW defaults TSX to be enabled at bootup.
 127                  * We may still need the TSX enable support
 128                  * during init for special cases like
 129                  * kexec after TSX is disabled.
 130                  */
 131                 tsx_enable();
 132
 133                 /*
 134                  * tsx_enable() will change the state of the
 135                  * RTM CPUID bit.  Force it here since it is now
 136                  * expected to be set.
 137                  */
 138                 setup_force_cpu_cap(X86_FEATURE_RTM);
 139         }
 140 }