To aid in speculation control, the LFENCE instruction will be turned into a serializing instruction. There is less performance impact using LFENCE in this way compared to MFENCE.
With LFENCE now being a serializing instruction, it can be used in rdtsc_ordered() in place of MFENCE_RDTSC. The other two patches in this series make this change and remove the MFENCE_RDTSC feature. The following patches are included in this series: - Make LFENCE a serializing instruction on AMD - Change over to LFENCE_RDTSC from MFENCE_RDTSC on AMD - Remove the MFENCE_RDTSC feature This patch series is based on tip:x86/pti. --- Tom Lendacky (3): x86/cpu/AMD: Make LFENCE a serializing instruction x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC x86/msr: Remove now unused definition of MFENCE_RDTSC feature arch/x86/include/asm/cpufeatures.h | 2 +- arch/x86/include/asm/msr-index.h | 2 ++ arch/x86/include/asm/msr.h | 3 +-- arch/x86/kernel/cpu/amd.c | 13 +++++++++++-- 4 files changed, 15 insertions(+), 5 deletions(-) -- Tom Lendacky