From: speck for Pawan Gupta Date: Wed, 9 Oct 2019 16:22:56 -0700 Subject: TAAv6 1 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 Reviewed-by: Mark Gross Reviewed-by: Tony Luck Tested-by: Neelima Krishnan --- 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 f58e6921cbf7..f45ca8aad98f 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -91,6 +91,7 @@ * physical address or cache type * without TLB invalidation. */ +#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) /* @@ -101,6 +102,10 @@ #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 fxeature */ +#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