Re: [Qemu-devel] [PATCH v2 1/2] x86/cpu: Add support for UMONITOR/UMWAIT/TPAUSE

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 24 May 2019 16:18:38 +0800
Tao Xu <tao3.xu@intel.com> wrote:

> UMONITOR, UMWAIT and TPAUSE are a set of user wait instructions.
> Availability of the user wait instructions is indicated by the presence
> of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX[5].
> 
> The patch 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
> 
> Co-developed-by: Jingqi Liu <jingqi.liu@intel.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
> Signed-off-by: Tao Xu <tao3.xu@intel.com>
> ---
>  linux-headers/linux/kvm.h |  1 +
>  target/i386/cpu.c         |  3 ++-
>  target/i386/cpu.h         |  1 +
>  target/i386/kvm.c         | 13 +++++++++++++
>  4 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> index c8423e760c..86cc2dbdd0 100644
> --- a/linux-headers/linux/kvm.h
> +++ b/linux-headers/linux/kvm.h
> @@ -993,6 +993,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_ARM_SVE 170
>  #define KVM_CAP_ARM_PTRAUTH_ADDRESS 171
>  #define KVM_CAP_ARM_PTRAUTH_GENERIC 172
> +#define KVM_CAP_ENABLE_USR_WAIT_PAUSE 173
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  

No comment on the actual change, but please split out any linux-header
changes so they can be replaced with a proper headers update when the
code is merged.