1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Intel Transactional Synchronization Extensions (TSX) control.
4 *
5 * Copyright (C) 2019-2021 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 #include <asm/cpu.h>
15
16 #include "cpu.h"
17
18 #undef pr_fmt
19 #define pr_fmt(fmt) "tsx: " fmt
20
21 enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
22
tsx_disable(void)23 static void tsx_disable(void)
24 {
25 u64 tsx;
26
27 rdmsrl(MSR_IA32_TSX_CTRL, tsx);
28
29 /* Force all transactions to immediately abort */
30 tsx |= TSX_CTRL_RTM_DISABLE;
31
32 /*
33 * Ensure TSX support is not enumerated in CPUID.
34 * This is visible to userspace and will ensure they
35 * do not waste resources trying TSX transactions that
36 * will always abort.
37 */
38 tsx |= TSX_CTRL_CPUID_CLEAR;
39
40 wrmsrl(MSR_IA32_TSX_CTRL, tsx);
41 }
42
tsx_enable(void)43 static void tsx_enable(void)
44 {
45 u64 tsx;
46
47 rdmsrl(MSR_IA32_TSX_CTRL, tsx);
48
49 /* Enable the RTM feature in the cpu */
50 tsx &= ~TSX_CTRL_RTM_DISABLE;
51
52 /*
53 * Ensure TSX support is enumerated in CPUID.
54 * This is visible to userspace and will ensure they
55 * can enumerate and use the TSX feature.
56 */
57 tsx &= ~TSX_CTRL_CPUID_CLEAR;
58
59 wrmsrl(MSR_IA32_TSX_CTRL, tsx);
60 }
61
x86_get_tsx_auto_mode(void)62 static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
63 {
64 if (boot_cpu_has_bug(X86_BUG_TAA))
65 return TSX_CTRL_DISABLE;
66
67 return TSX_CTRL_ENABLE;
68 }
69
70 /*
71 * Disabling TSX is not a trivial business.
72 *
73 * First of all, there's a CPUID bit: X86_FEATURE_RTM_ALWAYS_ABORT
74 * which says that TSX is practically disabled (all transactions are
75 * aborted by default). When that bit is set, the kernel unconditionally
76 * disables TSX.
77 *
78 * In order to do that, however, it needs to dance a bit:
79 *
80 * 1. The first method to disable it is through MSR_TSX_FORCE_ABORT and
81 * the MSR is present only when *two* CPUID bits are set:
82 *
83 * - X86_FEATURE_RTM_ALWAYS_ABORT
84 * - X86_FEATURE_TSX_FORCE_ABORT
85 *
86 * 2. The second method is for CPUs which do not have the above-mentioned
87 * MSR: those use a different MSR - MSR_IA32_TSX_CTRL and disable TSX
88 * through that one. Those CPUs can also have the initially mentioned
89 * CPUID bit X86_FEATURE_RTM_ALWAYS_ABORT set and for those the same strategy
90 * applies: TSX gets disabled unconditionally.
91 *
92 * When either of the two methods are present, the kernel disables TSX and
93 * clears the respective RTM and HLE feature flags.
94 *
95 * An additional twist in the whole thing presents late microcode loading
96 * which, when done, may cause for the X86_FEATURE_RTM_ALWAYS_ABORT CPUID
97 * bit to be set after the update.
98 *
99 * A subsequent hotplug operation on any logical CPU except the BSP will
100 * cause for the supported CPUID feature bits to get re-detected and, if
101 * RTM and HLE get cleared all of a sudden, but, userspace did consult
102 * them before the update, then funny explosions will happen. Long story
103 * short: the kernel doesn't modify CPUID feature bits after booting.
104 *
105 * That's why, this function's call in init_intel() doesn't clear the
106 * feature flags.
107 */
tsx_clear_cpuid(void)108 static void tsx_clear_cpuid(void)
109 {
110 u64 msr;
111
112 /*
113 * MSR_TFA_TSX_CPUID_CLEAR bit is only present when both CPUID
114 * bits RTM_ALWAYS_ABORT and TSX_FORCE_ABORT are present.
115 */
116 if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) &&
117 boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
118 rdmsrl(MSR_TSX_FORCE_ABORT, msr);
119 msr |= MSR_TFA_TSX_CPUID_CLEAR;
120 wrmsrl(MSR_TSX_FORCE_ABORT, msr);
121 } else if (cpu_feature_enabled(X86_FEATURE_MSR_TSX_CTRL)) {
122 rdmsrl(MSR_IA32_TSX_CTRL, msr);
123 msr |= TSX_CTRL_CPUID_CLEAR;
124 wrmsrl(MSR_IA32_TSX_CTRL, msr);
125 }
126 }
127
128 /*
129 * Disable TSX development mode
130 *
131 * When the microcode released in Feb 2022 is applied, TSX will be disabled by
132 * default on some processors. MSR 0x122 (TSX_CTRL) and MSR 0x123
133 * (IA32_MCU_OPT_CTRL) can be used to re-enable TSX for development, doing so is
134 * not recommended for production deployments. In particular, applying MD_CLEAR
135 * flows for mitigation of the Intel TSX Asynchronous Abort (TAA) transient
136 * execution attack may not be effective on these processors when Intel TSX is
137 * enabled with updated microcode.
138 */
tsx_dev_mode_disable(void)139 static void tsx_dev_mode_disable(void)
140 {
141 u64 mcu_opt_ctrl;
142
143 /* Check if RTM_ALLOW exists */
144 if (!boot_cpu_has_bug(X86_BUG_TAA) ||
145 !cpu_feature_enabled(X86_FEATURE_MSR_TSX_CTRL) ||
146 !cpu_feature_enabled(X86_FEATURE_SRBDS_CTRL))
147 return;
148
149 rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl);
150
151 if (mcu_opt_ctrl & RTM_ALLOW) {
152 mcu_opt_ctrl &= ~RTM_ALLOW;
153 wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl);
154 setup_force_cpu_cap(X86_FEATURE_RTM_ALWAYS_ABORT);
155 }
156 }
157
tsx_init(void)158 void __init tsx_init(void)
159 {
160 char arg[5] = {};
161 int ret;
162
163 tsx_dev_mode_disable();
164
165 /*
166 * Hardware will always abort a TSX transaction when the CPUID bit
167 * RTM_ALWAYS_ABORT is set. In this case, it is better not to enumerate
168 * CPUID.RTM and CPUID.HLE bits. Clear them here.
169 */
170 if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT)) {
171 tsx_ctrl_state = TSX_CTRL_RTM_ALWAYS_ABORT;
172 tsx_clear_cpuid();
173 setup_clear_cpu_cap(X86_FEATURE_RTM);
174 setup_clear_cpu_cap(X86_FEATURE_HLE);
175 return;
176 }
177
178 /*
179 * TSX is controlled via MSR_IA32_TSX_CTRL. However, support for this
180 * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
181 *
182 * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
183 * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
184 * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
185 * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
186 * tsx= cmdline requests will do nothing on CPUs without
187 * MSR_IA32_TSX_CTRL support.
188 */
189 if (x86_read_arch_cap_msr() & ARCH_CAP_TSX_CTRL_MSR) {
190 setup_force_cpu_cap(X86_FEATURE_MSR_TSX_CTRL);
191 } else {
192 tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED;
193 return;
194 }
195
196 ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
197 if (ret >= 0) {
198 if (!strcmp(arg, "on")) {
199 tsx_ctrl_state = TSX_CTRL_ENABLE;
200 } else if (!strcmp(arg, "off")) {
201 tsx_ctrl_state = TSX_CTRL_DISABLE;
202 } else if (!strcmp(arg, "auto")) {
203 tsx_ctrl_state = x86_get_tsx_auto_mode();
204 } else {
205 tsx_ctrl_state = TSX_CTRL_DISABLE;
206 pr_err("invalid option, defaulting to off\n");
207 }
208 } else {
209 /* tsx= not provided */
210 if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
211 tsx_ctrl_state = x86_get_tsx_auto_mode();
212 else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
213 tsx_ctrl_state = TSX_CTRL_DISABLE;
214 else
215 tsx_ctrl_state = TSX_CTRL_ENABLE;
216 }
217
218 if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
219 tsx_disable();
220
221 /*
222 * tsx_disable() will change the state of the RTM and HLE CPUID
223 * bits. Clear them here since they are now expected to be not
224 * set.
225 */
226 setup_clear_cpu_cap(X86_FEATURE_RTM);
227 setup_clear_cpu_cap(X86_FEATURE_HLE);
228 } else if (tsx_ctrl_state == TSX_CTRL_ENABLE) {
229
230 /*
231 * HW defaults TSX to be enabled at bootup.
232 * We may still need the TSX enable support
233 * during init for special cases like
234 * kexec after TSX is disabled.
235 */
236 tsx_enable();
237
238 /*
239 * tsx_enable() will change the state of the RTM and HLE CPUID
240 * bits. Force them here since they are now expected to be set.
241 */
242 setup_force_cpu_cap(X86_FEATURE_RTM);
243 setup_force_cpu_cap(X86_FEATURE_HLE);
244 }
245 }
246
tsx_ap_init(void)247 void tsx_ap_init(void)
248 {
249 tsx_dev_mode_disable();
250
251 if (tsx_ctrl_state == TSX_CTRL_ENABLE)
252 tsx_enable();
253 else if (tsx_ctrl_state == TSX_CTRL_DISABLE)
254 tsx_disable();
255 else if (tsx_ctrl_state == TSX_CTRL_RTM_ALWAYS_ABORT)
256 /* See comment over that function for more details. */
257 tsx_clear_cpuid();
258 }
259