[MODERATED] [PATCH v6 1/9] TAAv6 1

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: speck@linutronix.de
Subject: [MODERATED] [PATCH v6 1/9] TAAv6 1
Date: Wed, 9 Oct 2019 16:22:56 -0700	[thread overview]
Message-ID: <=?utf-8?q?=3C4102a059c94384a1cbb2c1919eb446683cce9399=2E157065?= =?utf-8?q?8888=2Egit=2Epawan=2Ekumar=2Egupta=40linux=2Eintel=2Ecom=3E?=> (raw)
In-Reply-To: <cover.1570658888.git.pawan.kumar.gupta@linux.intel.com>

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.  [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 but still enumerated as present by CPUID(EAX=7).EBX{bit4}.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
---
 arch/x86/include/asm/msr-index.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 271d837d69a8..45b6705d9f71 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -93,6 +93,7 @@
 						  * Microarchitectural Data
 						  * Sampling (MDS) vulnerabilities.
 						  */
+#define ARCH_CAP_TSX_CTRL_MSR		BIT(7)	/* MSR for TSX control is available. */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*
@@ -103,6 +104,10 @@
 #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		BIT(0)	/* Disable RTM feature */
+#define TSX_CTRL_CPUID_CLEAR		BIT(1)	/* Disable TSX enumeration */
+
 #define MSR_IA32_SYSENTER_CS		0x00000174
 #define MSR_IA32_SYSENTER_ESP		0x00000175
 #define MSR_IA32_SYSENTER_EIP		0x00000176
-- 
2.20.1
