[PATCH 3.16 03/25] x86/msr: Add the IA32_TSX_CTRL MSR

[Ben Hutchings]

3.16.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>

commit c2955f270a84762343000f103e0640d29c7a96f3 upstream.

Transactional Synchronization Extensions (TSX) may be used on certain
processors as part of a speculative side channel attack.  A microcode
update for existing processors that are vulnerable to this attack will
add a new MSR - IA32_TSX_CTRL to allow the system administrator the
option to disable TSX as one of the possible mitigations.

The CPUs which get this new MSR after a microcode upgrade are the ones
which do not set MSR_IA32_ARCH_CAPABILITIES.MDS_NO (bit 5) because those
CPUs have CPUID.MD_CLEAR, i.e., the VERW implementation which clears all
CPU buffers takes care of the TAA case as well.

  [ Note that future processors that are not vulnerable will also
    support the IA32_TSX_CTRL MSR. ]

Add defines for the new IA32_TSX_CTRL MSR and its bits.

TSX has two sub-features:

1. Restricted Transactional Memory (RTM) is an explicitly-used feature
   where new instructions begin and end TSX transactions.
2. Hardware Lock Elision (HLE) is implicitly used when certain kinds of
   "old" style locks are used by software.

Bit 7 of the IA32_ARCH_CAPABILITIES indicates the presence of the
IA32_TSX_CTRL MSR.

There are two control bits in IA32_TSX_CTRL MSR:

  Bit 0: When set, it disables the Restricted Transactional Memory (RTM)
         sub-feature of TSX (will force all transactions to abort on the
	 XBEGIN instruction).

  Bit 1: When set, it disables the enumeration of the RTM and HLE feature
         (i.e. it will make CPUID(EAX=7).EBX{bit4} and
	  CPUID(EAX=7).EBX{bit11} read as 0).

The other TSX sub-feature, Hardware Lock Elision (HLE), is
unconditionally disabled by the new microcode but still enumerated
as present by CPUID(EAX=7).EBX{bit4}, unless disabled by
IA32_TSX_CTRL_MSR[1] - TSX_CTRL_CPUID_CLEAR.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Neelima Krishnan <neelima.krishnan@xxxxxxxxx>
Reviewed-by: Mark Gross <mgross@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - Don't use BIT() in msr-index.h because it's a UAPI header
 - Adjust filename, context, indentation]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/include/uapi/asm/msr-index.h | 5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/include/uapi/asm/msr-index.h
+++ b/arch/x86/include/uapi/asm/msr-index.h
@@ -70,10 +70,15 @@
 						    * Microarchitectural Data
 						    * Sampling (MDS) vulnerabilities.
 						    */
+#define ARCH_CAP_TSX_CTRL_MSR		(1UL << 7) /* MSR for TSX control is available. */
 
 #define MSR_IA32_BBL_CR_CTL		0x00000119
 #define MSR_IA32_BBL_CR_CTL3		0x0000011e
 
+#define MSR_IA32_TSX_CTRL		0x00000122
+#define TSX_CTRL_RTM_DISABLE		(1UL << 0) /* Disable RTM feature */
+#define TSX_CTRL_CPUID_CLEAR		(1UL << 1) /* Disable TSX enumeration */
+
 #define MSR_IA32_SYSENTER_CS		0x00000174
 #define MSR_IA32_SYSENTER_ESP		0x00000175
 #define MSR_IA32_SYSENTER_EIP		0x00000176