3.16.56-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Tom Lendacky thomas.lendacky@amd.com
commit e4d0e84e490790798691aaa0f2e598637f1867ec upstream.
To aid in speculation control, make LFENCE a serializing instruction since it has less overhead than MFENCE. This is done by setting bit 1 of MSR 0xc0011029 (DE_CFG). Some families that support LFENCE do not have this MSR. For these families, the LFENCE instruction is already serializing.
Signed-off-by: Tom Lendacky thomas.lendacky@amd.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Reviewed-by: Borislav Petkov bp@suse.de Cc: Peter Zijlstra peterz@infradead.org Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Dave Hansen dave.hansen@intel.com Cc: Borislav Petkov bp@alien8.de Cc: Dan Williams dan.j.williams@intel.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Greg Kroah-Hartman gregkh@linux-foundation.org Cc: David Woodhouse dwmw@amazon.co.uk Cc: Paul Turner pjt@google.com Link: https://lkml.kernel.org/r/20180108220921.12580.71694.stgit@tlendack-t1.amdof... [bwh: Backported to 3.16: adjust filename, context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/include/uapi/asm/msr-index.h | 2 ++ arch/x86/kernel/cpu/amd.c | 10 ++++++++++ 2 files changed, 12 insertions(+)
--- a/arch/x86/include/uapi/asm/msr-index.h +++ b/arch/x86/include/uapi/asm/msr-index.h @@ -223,6 +223,8 @@ #define FAM10H_MMIO_CONF_BASE_MASK 0xfffffffULL #define FAM10H_MMIO_CONF_BASE_SHIFT 20 #define MSR_FAM10H_NODE_ID 0xc001100c +#define MSR_F10H_DECFG 0xc0011029 +#define MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT 1
/* K8 MSRs */ #define MSR_K8_TOP_MEM1 0xc001001a --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -673,6 +673,16 @@ static void init_amd(struct cpuinfo_x86 set_cpu_cap(c, X86_FEATURE_K8);
if (cpu_has_xmm2) { + /* + * A serializing LFENCE has less overhead than MFENCE, so + * use it for execution serialization. On families which + * don't have that MSR, LFENCE is already serializing. + * msr_set_bit() uses the safe accessors, too, even if the MSR + * is not present. + */ + msr_set_bit(MSR_F10H_DECFG, + MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT); + /* MFENCE stops RDTSC speculation */ set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC); }