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Subject[PATCH v8 0/3] KVM: x86: Enable user wait instructions
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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[5].

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:
v8:
Add vmx_waitpkg_supported() helper (Sean)
Add an accessor to expose umwait_control_cached (Sean)
Set msr_ia32_umwait_control in vcpu_vmx u32 and raise #GP when
[63:32] is set when rdmsr. (Sean)
Introduce a common exit helper handle_unexpected_vmexit (Sean)
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: Introduce handle_unexpected_vmexit and handle WAITPKG vmexit

arch/x86/include/asm/vmx.h | 1 +
arch/x86/include/uapi/asm/vmx.h | 6 ++-
arch/x86/kernel/cpu/umwait.c | 6 +++
arch/x86/kvm/cpuid.c | 2 +-
arch/x86/kvm/vmx/capabilities.h | 6 +++
arch/x86/kvm/vmx/nested.c | 5 ++
arch/x86/kvm/vmx/vmx.c | 83 ++++++++++++++++++++++++++-------
arch/x86/kvm/vmx/vmx.h | 9 ++++
arch/x86/kvm/x86.c | 1 +
9 files changed, 101 insertions(+), 18 deletions(-)

--
2.20.1

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