[MODERATED] [PATCH v5 03/11] TAAv5 3

Disable TSX by default on bootup. If IA32_TSX_CTRL MSR is not present,
TSX state stays NOT_SUPPORTED which is the compile time default,
otherwise change TSX state to DISABLE. This is because on certain
processsors TSX may be used as a part of a speculative side channel
attack.

Signed-off-by: Pawan Gupta <[email protected]>
Reviewed-by: Mark Gross <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
Tested-by: Neelima Krishnan <[email protected]>
---
 arch/x86/kernel/cpu/Makefile |  2 +-
 arch/x86/kernel/cpu/cpu.h    |  4 ++
 arch/x86/kernel/cpu/intel.c  |  2 +
 arch/x86/kernel/cpu/tsx.c    | 72 ++++++++++++++++++++++++++++++++++++
 4 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/kernel/cpu/tsx.c

diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index d7a1e5a9331c..890f60083eca 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -30,7 +30,7 @@ obj-$(CONFIG_PROC_FS)	+= proc.o
 obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
 
 ifdef CONFIG_CPU_SUP_INTEL
-obj-y			+= intel.o intel_pconfig.o
+obj-y			+= intel.o intel_pconfig.o tsx.o
 obj-$(CONFIG_PM)	+= intel_epb.o
 endif
 obj-$(CONFIG_CPU_SUP_AMD)		+= amd.o
diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index c0e2407abdd6..d864ec4180cc 100644
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -62,4 +62,8 @@ unsigned int aperfmperf_get_khz(int cpu);
 
 extern void x86_spec_ctrl_setup_ap(void);
 
+extern void tsx_init(struct cpuinfo_x86 *c);
+
+extern u64 read_ia32_arch_cap(void);
+
 #endif /* ARCH_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 8d6d92ebeb54..b1d6c96f6b88 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -761,6 +761,8 @@ static void init_intel(struct cpuinfo_x86 *c)
 		detect_tme(c);
 
 	init_intel_misc_features(c);
+
+	tsx_init(c);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
new file mode 100644
index 000000000000..c549750dd7c8
--- /dev/null
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel Transactional Synchronization Extensions (TSX) control.
+ *
+ * Copyright (C) 2019 Intel Corporation
+ *
+ * Author:
+ *	Pawan Gupta <[email protected]>
+ */
+
+#include <linux/processor.h>
+#include <linux/cpufeature.h>
+
+#include "cpu.h"
+
+static enum tsx_ctrl_states {
+	TSX_CTRL_ENABLE,
+	TSX_CTRL_DISABLE,
+	TSX_CTRL_NOT_SUPPORTED,
+} tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED;
+
+static void tsx_disable(void)
+{
+	u64 tsx;
+
+	rdmsrl(MSR_IA32_TSX_CTRL, tsx);
+
+	/* Force all transactions to immediately abort */
+	tsx |= TSX_CTRL_RTM_DISABLE;
+	/*
+	 * Ensure TSX support is not enumerated in CPUID.
+	 * This is visible to userspace and will ensure they
+	 * do not waste resources trying TSX transactions that
+	 * will always abort.
+	 */
+	tsx |= TSX_CTRL_CPUID_CLEAR;
+
+	wrmsrl(MSR_IA32_TSX_CTRL, tsx);
+}
+
+static bool tsx_ctrl_is_supported(void)
+{
+	u64 ia32_cap = read_ia32_arch_cap();
+
+	/*
+	 * TSX is controlled via MSR_IA32_TSX_CTRL.  However,
+	 * support for this MSR is enumerated by ARCH_CAP_TSX_MSR bit
+	 * in MSR_IA32_ARCH_CAPABILITIES.
+	 */
+	return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
+}
+
+void tsx_init(struct cpuinfo_x86 *c)
+{
+	if (!tsx_ctrl_is_supported())
+		return;
+
+	/*
+	 * Default to TSX_CTRL_DISABLE. This is because on certain processors
+	 * TSX may be used as part of a speculative side channel attack.
+	 */
+	tsx_ctrl_state = TSX_CTRL_DISABLE;
+
+	tsx_disable();
+	/*
+	 * tsx_disable() will change the state of the
+	 * RTM CPUID bit.  Clear it here since it is now
+	 * expected to be not set.
+	 */
+	clear_cpu_cap(c, X86_FEATURE_RTM);
+	setup_clear_cpu_cap(X86_FEATURE_RTM);
+}
-- 
2.20.1