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

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

On 6/4/2019 10:34 PM, Cornelia Huck wrote:
> 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.
> 
Thank you for your review, I will update this patch when the kvm patch 
change a lot.