Re: [PATCH v5 0/2] x86: Enable user wait instructions

[Tao Xu <tao3.xu@intel.com>]

Ping for comments :)

On 9/29/2019 9:57 AM, Xu, Tao3 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 in kvm and provide a capability to
> enable it. Use kvm capability to enable UMONITOR, UMWAIT and TPAUSE when
> QEMU use "-overcommit cpu-pm=on, a VM can use UMONITOR, UMWAIT and TPAUSE
> instructions. 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). Otherwise, UMONITOR, UMWAIT and TPAUSE cause
> an invalid-opcode exception(#UD).
> 
> The release document ref below link:
> https://software.intel.com/sites/default/files/\
> managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf
> 
> Changelog:
> v5:
> 	Remove CPUID_7_0_ECX_WAITPKG if enable_cpu_pm is not set. (Paolo)
> v4:
> 	Set IA32_UMWAIT_CONTROL 32bits
> v3:
> 	Simplify the patches, expose user wait instructions when the guest
> 	has CPUID (Paolo)
> v2:
> 	Separated from the series
> 	https://www.mail-archive.com/qemu-devel@nongnu.org/msg549526.html
> 	Use kvm capability to enable UMONITOR, UMWAIT and TPAUSE when
> 	QEMU use "-overcommit cpu-pm=on"	
> v1:
> 	Sent out with MOVDIRI/MOVDIR64B instructions patches
> 
> Tao Xu (2):
>    x86/cpu: Add support for UMONITOR/UMWAIT/TPAUSE
>    target/i386: Add support for save/load IA32_UMWAIT_CONTROL MSR
> 
>   target/i386/cpu.c     |  3 ++-
>   target/i386/cpu.h     |  3 +++
>   target/i386/kvm.c     | 19 +++++++++++++++++++
>   target/i386/machine.c | 20 ++++++++++++++++++++
>   4 files changed, 44 insertions(+), 1 deletion(-)
>