UMONITOR, UMWAIT and TPAUSE are a set of user wait instructions. UMONITOR arms address monitoring hardware using an address. A store to an address within the specified address range triggers the monitoring hardware to wake up the processor waiting in umwait.
UMWAIT instructs the processor to enter an implementation-dependent optimized state while monitoring a range of addresses. The optimized state may be either a light-weight power/performance optimized state (c0.1 state) or an improved power/performance optimized state (c0.2 state). TPAUSE instructs the processor to enter an implementation-dependent optimized state c0.1 or c0.2 state and wake up when time-stamp counter reaches specified timeout. Availability of the user wait instructions is indicated by the presence of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX. The patches enable the umonitor, umwait and tpause features in KVM. Because umwait and tpause can put a (psysical) CPU into a power saving state, by default we dont't expose it to kvm and enable it only when guest CPUID has it. If the instruction causes a delay, the amount of time delayed is called here the physical delay. The physical delay is first computed by determining the virtual delay (the time to delay relative to the VM’s timestamp counter). The release document ref below link: Intel 64 and IA-32 Architectures Software Developer's Manual, https://software.intel.com/sites/default/files/\ managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf Changelog: v7: Add nested support for user wait instructions (Paolo) Use the test on vmx->secondary_exec_control to replace guest_cpuid_has (Paolo) v6: add check msr_info->host_initiated in get/set msr(Xiaoyao) restore the atomic_switch_umwait_control_msr()(Xiaoyao) Tao Xu (3): KVM: x86: add support for user wait instructions KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL KVM: vmx: handle vm-exit for UMWAIT and TPAUSE arch/x86/include/asm/vmx.h | 1 + arch/x86/include/uapi/asm/vmx.h | 6 ++- arch/x86/kernel/cpu/umwait.c | 3 +- arch/x86/kvm/cpuid.c | 2 +- arch/x86/kvm/vmx/nested.c | 4 ++ arch/x86/kvm/vmx/vmx.c | 69 +++++++++++++++++++++++++++++++++ arch/x86/kvm/vmx/vmx.h | 9 +++++ arch/x86/kvm/x86.c | 1 + 8 files changed, 92 insertions(+), 3 deletions(-) -- 2.20.1