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SubjectRe: [PATCH v8 0/3] KVM: x86: Enable user wait instructions
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Ping for comments :)

On 7/16/2019 2:55 PM, Tao Xu wrote:
> 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(-)
>

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