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 #undef pr_fmt
  18 #define pr_fmt(fmt) "tsx: " fmt
  19
  20 enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
  21
  22 void tsx_disable(void)
  23 {
  24         u64 tsx;
  25
  26         rdmsrl(MSR_IA32_TSX_CTRL, tsx);
  27
  28         /* Force all transactions to immediately abort */
  29         tsx |= TSX_CTRL_RTM_DISABLE;
  30
  31         /*
  32          * Ensure TSX support is not enumerated in CPUID.
  33          * This is visible to userspace and will ensure they
  34          * do not waste resources trying TSX transactions that
  35          * will always abort.
  36          */
  37         tsx |= TSX_CTRL_CPUID_CLEAR;
  38
  39         wrmsrl(MSR_IA32_TSX_CTRL, tsx);
  40 }
  41
  42 void tsx_enable(void)
  43 {
  44         u64 tsx;
  45
  46         rdmsrl(MSR_IA32_TSX_CTRL, tsx);
  47
  48         /* Enable the RTM feature in the cpu */
  49         tsx &= ~TSX_CTRL_RTM_DISABLE;
  50
  51         /*
  52          * Ensure TSX support is enumerated in CPUID.
  53          * This is visible to userspace and will ensure they
  54          * can enumerate and use the TSX feature.
  55          */
  56         tsx &= ~TSX_CTRL_CPUID_CLEAR;
  57
  58         wrmsrl(MSR_IA32_TSX_CTRL, tsx);
  59 }
  60
  61 static bool __init tsx_ctrl_is_supported(void)
  62 {
  63         u64 ia32_cap = x86_read_arch_cap_msr();
  64
  65         /*
  66          * TSX is controlled via MSR_IA32_TSX_CTRL.  However, support for this
  67          * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
  68          *
  69          * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
  70          * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
  71          * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
  72          * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
  73          * tsx= cmdline requests will do nothing on CPUs without
  74          * MSR_IA32_TSX_CTRL support.
  75          */
  76         return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
  77 }
  78
  79 static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
  80 {
  81         if (boot_cpu_has_bug(X86_BUG_TAA))
  82                 return TSX_CTRL_DISABLE;
  83
  84         return TSX_CTRL_ENABLE;
  85 }
  86
  87 void __init tsx_init(void)
  88 {
  89         char arg[5] = {};
  90         int ret;
  91
  92         if (!tsx_ctrl_is_supported())
  93                 return;
  94
  95         ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
  96         if (ret >= 0) {
  97                 if (!strcmp(arg, "on")) {
  98                         tsx_ctrl_state = TSX_CTRL_ENABLE;
  99                 } else if (!strcmp(arg, "off")) {
 100                         tsx_ctrl_state = TSX_CTRL_DISABLE;
 101                 } else if (!strcmp(arg, "auto")) {
 102                         tsx_ctrl_state = x86_get_tsx_auto_mode();
 103                 } else {
 104                         tsx_ctrl_state = TSX_CTRL_DISABLE;
 105                         pr_err("invalid option, defaulting to off\n");
 106                 }
 107         } else {
 108                 /* tsx= not provided */
 109                 if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
 110                         tsx_ctrl_state = x86_get_tsx_auto_mode();
 111                 else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
 112                         tsx_ctrl_state = TSX_CTRL_DISABLE;
 113                 else
 114                         tsx_ctrl_state = TSX_CTRL_ENABLE;
 115         }
 116
 117         if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
 118                 tsx_disable();
 119
 120                 /*
 121                  * tsx_disable() will change the state of the
 122                  * RTM CPUID bit.  Clear it here since it is now
 123                  * expected to be not set.
 124                  */
 125                 setup_clear_cpu_cap(X86_FEATURE_RTM);
 126         } else if (tsx_ctrl_state == TSX_CTRL_ENABLE) {
 127
 128                 /*
 129                  * HW defaults TSX to be enabled at bootup.
 130                  * We may still need the TSX enable support
 131                  * during init for special cases like
 132                  * kexec after TSX is disabled.
 133                  */
 134                 tsx_enable();
 135
 136                 /*
 137                  * tsx_enable() will change the state of the
 138                  * RTM CPUID bit.  Force it here since it is now
 139                  * expected to be set.
 140                  */
 141                 setup_force_cpu_cap(X86_FEATURE_RTM);
 142         }
 143 }