linux-kernel - RE: [PATCH 1/3] KVM: x86: expose UMWAIT/UMONITOR/TPAUSE CPU features into VM.

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Date:   Mon, 20 Aug 2018 12:36:52 +0000
From:   "Liu, Jingqi" <jingqi.liu@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Wang, Wei W" <wei.w.wang@...el.com>
Subject: RE: [PATCH 1/3] KVM: x86: expose UMWAIT/UMONITOR/TPAUSE CPU
 features into VM.

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@...hat.com]
> Sent: Monday, August 20, 2018 6:16 PM
> To: Liu, Jingqi <jingqi.liu@...el.com>; rkrcmar@...hat.com; tglx@...utronix.de;
> mingo@...hat.com; hpa@...or.com
> Cc: x86@...nel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Wang,
> Wei W <wei.w.wang@...el.com>
> Subject: Re: [PATCH 1/3] KVM: x86: expose UMWAIT/UMONITOR/TPAUSE CPU
> features into VM.
> 
> On 10/07/2018 10:54, Jingqi Liu 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].
> >
> > This patch exposes the umonitor,umwait, and tpause features to the guest.
> >
> > The release document ref below link:
> > https://software.intel.com/sites/default/files/managed/c5/15/\
> > architecture-instruction-set-extensions-programming-reference.pdf
> > This patch has a dependency on https://lkml.org/lkml/2018/6/15/657.
> >
> > Signed-off-by: Jingqi Liu <jingqi.liu@...el.com>
> 
> Hi Jingqi, you also need to track and save/restore IA32_UMWAIT_CONTROL.

Yes, I'll handle IA32_UMWAIT_CONTROL in the second version.
Thanks for your review.

> 
> Thanks,
> 
> Paolo
> 
> > ---
> >  arch/x86/kvm/cpuid.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index
> > 7e042e3..e16c05e 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -406,7 +406,7 @@ static inline int __do_cpuid_ent(struct
> kvm_cpuid_entry2 *entry, u32 function,
> >  		F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ |
> >  		F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI)
> |
> >  		F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) |
> F(AVX512_BITALG) |
> > -		F(CLDEMOTE);
> > +		F(CLDEMOTE) | F(WAITPKG);
> >
> >  	/* cpuid 7.0.edx*/
> >  	const u32 kvm_cpuid_7_0_edx_x86_features =
> >