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Diffstat (limited to 'arch/x86/kernel/cpu/tsx.c')
-rw-r--r--arch/x86/kernel/cpu/tsx.c104
1 files changed, 94 insertions, 10 deletions
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index 9c7a5f049292..ec7bbac3a9f2 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -19,7 +19,7 @@
enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
-void tsx_disable(void)
+static void tsx_disable(void)
{
u64 tsx;
@@ -39,7 +39,7 @@ void tsx_disable(void)
wrmsrl(MSR_IA32_TSX_CTRL, tsx);
}
-void tsx_enable(void)
+static void tsx_enable(void)
{
u64 tsx;
@@ -58,7 +58,7 @@ void tsx_enable(void)
wrmsrl(MSR_IA32_TSX_CTRL, tsx);
}
-static bool __init tsx_ctrl_is_supported(void)
+static bool tsx_ctrl_is_supported(void)
{
u64 ia32_cap = x86_read_arch_cap_msr();
@@ -84,7 +84,45 @@ static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
return TSX_CTRL_ENABLE;
}
-void tsx_clear_cpuid(void)
+/*
+ * Disabling TSX is not a trivial business.
+ *
+ * First of all, there's a CPUID bit: X86_FEATURE_RTM_ALWAYS_ABORT
+ * which says that TSX is practically disabled (all transactions are
+ * aborted by default). When that bit is set, the kernel unconditionally
+ * disables TSX.
+ *
+ * In order to do that, however, it needs to dance a bit:
+ *
+ * 1. The first method to disable it is through MSR_TSX_FORCE_ABORT and
+ * the MSR is present only when *two* CPUID bits are set:
+ *
+ * - X86_FEATURE_RTM_ALWAYS_ABORT
+ * - X86_FEATURE_TSX_FORCE_ABORT
+ *
+ * 2. The second method is for CPUs which do not have the above-mentioned
+ * MSR: those use a different MSR - MSR_IA32_TSX_CTRL and disable TSX
+ * through that one. Those CPUs can also have the initially mentioned
+ * CPUID bit X86_FEATURE_RTM_ALWAYS_ABORT set and for those the same strategy
+ * applies: TSX gets disabled unconditionally.
+ *
+ * When either of the two methods are present, the kernel disables TSX and
+ * clears the respective RTM and HLE feature flags.
+ *
+ * An additional twist in the whole thing presents late microcode loading
+ * which, when done, may cause for the X86_FEATURE_RTM_ALWAYS_ABORT CPUID
+ * bit to be set after the update.
+ *
+ * A subsequent hotplug operation on any logical CPU except the BSP will
+ * cause for the supported CPUID feature bits to get re-detected and, if
+ * RTM and HLE get cleared all of a sudden, but, userspace did consult
+ * them before the update, then funny explosions will happen. Long story
+ * short: the kernel doesn't modify CPUID feature bits after booting.
+ *
+ * That's why, this function's call in init_intel() doesn't clear the
+ * feature flags.
+ */
+static void tsx_clear_cpuid(void)
{
u64 msr;
@@ -97,6 +135,39 @@ void tsx_clear_cpuid(void)
rdmsrl(MSR_TSX_FORCE_ABORT, msr);
msr |= MSR_TFA_TSX_CPUID_CLEAR;
wrmsrl(MSR_TSX_FORCE_ABORT, msr);
+ } else if (tsx_ctrl_is_supported()) {
+ rdmsrl(MSR_IA32_TSX_CTRL, msr);
+ msr |= TSX_CTRL_CPUID_CLEAR;
+ wrmsrl(MSR_IA32_TSX_CTRL, msr);
+ }
+}
+
+/*
+ * Disable TSX development mode
+ *
+ * When the microcode released in Feb 2022 is applied, TSX will be disabled by
+ * default on some processors. MSR 0x122 (TSX_CTRL) and MSR 0x123
+ * (IA32_MCU_OPT_CTRL) can be used to re-enable TSX for development, doing so is
+ * not recommended for production deployments. In particular, applying MD_CLEAR
+ * flows for mitigation of the Intel TSX Asynchronous Abort (TAA) transient
+ * execution attack may not be effective on these processors when Intel TSX is
+ * enabled with updated microcode.
+ */
+static void tsx_dev_mode_disable(void)
+{
+ u64 mcu_opt_ctrl;
+
+ /* Check if RTM_ALLOW exists */
+ if (!boot_cpu_has_bug(X86_BUG_TAA) || !tsx_ctrl_is_supported() ||
+ !cpu_feature_enabled(X86_FEATURE_SRBDS_CTRL))
+ return;
+
+ rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl);
+
+ if (mcu_opt_ctrl & RTM_ALLOW) {
+ mcu_opt_ctrl &= ~RTM_ALLOW;
+ wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl);
+ setup_force_cpu_cap(X86_FEATURE_RTM_ALWAYS_ABORT);
}
}
@@ -105,14 +176,14 @@ void __init tsx_init(void)
char arg[5] = {};
int ret;
+ tsx_dev_mode_disable();
+
/*
- * Hardware will always abort a TSX transaction if both CPUID bits
- * RTM_ALWAYS_ABORT and TSX_FORCE_ABORT are set. In this case, it is
- * better not to enumerate CPUID.RTM and CPUID.HLE bits. Clear them
- * here.
+ * Hardware will always abort a TSX transaction when the CPUID bit
+ * RTM_ALWAYS_ABORT is set. In this case, it is better not to enumerate
+ * CPUID.RTM and CPUID.HLE bits. Clear them here.
*/
- if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) &&
- boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
+ if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT)) {
tsx_ctrl_state = TSX_CTRL_RTM_ALWAYS_ABORT;
tsx_clear_cpuid();
setup_clear_cpu_cap(X86_FEATURE_RTM);
@@ -175,3 +246,16 @@ void __init tsx_init(void)
setup_force_cpu_cap(X86_FEATURE_HLE);
}
}
+
+void tsx_ap_init(void)
+{
+ tsx_dev_mode_disable();
+
+ if (tsx_ctrl_state == TSX_CTRL_ENABLE)
+ tsx_enable();
+ else if (tsx_ctrl_state == TSX_CTRL_DISABLE)
+ tsx_disable();
+ else if (tsx_ctrl_state == TSX_CTRL_RTM_ALWAYS_ABORT)
+ /* See comment over that function for more details. */
+ tsx_clear_cpuid();
+}