linux-kernel - Re: [PATCH v4 1/4] KVM: X86: Add vCPU running/preempted state

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Message-ID: <d096d9d1-dc6b-a9d6-f745-022a8336d1a3@redhat.com>
Date:   Tue, 14 Nov 2017 17:45:30 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v4 1/4] KVM: X86: Add vCPU running/preempted state

On 13.11.2017 01:33, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> This patch reuses the preempted field in kvm_steal_time, and will export
> the vcpu running/pre-empted information to the guest from host. This will
> enable guest to intelligently send ipi to running vcpus and set flag for
> pre-empted vcpus. This will prevent waiting for vcpus that are not running.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/include/uapi/asm/kvm_para.h | 3 +++
>  arch/x86/kernel/kvm.c                | 2 +-
>  arch/x86/kvm/x86.c                   | 4 ++--
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 554aa8f..bf17b30 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -51,6 +51,9 @@ struct kvm_steal_time {
>  	__u32 pad[11];
>  };
>  
> +#define KVM_VCPU_NOT_PREEMPTED      (0 << 0)
> +#define KVM_VCPU_PREEMPTED          (1 << 0)

These should have a prefix that makes it obvious that they are used
for kvm_steal_time/preempted.

What about renaming preempted to "flags" or something like that.
Then we could have

KVM_STEAL_TIME_(FLAG_)PREEMPTED
KVM_STEAL_TIME_(FLAG_)NOT_PREEMPTED

> +
>  #define KVM_CLOCK_PAIRING_WALLCLOCK 0
>  struct kvm_clock_pairing {
>  	__s64 sec;
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 8bb9594..1b1b641 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -608,7 +608,7 @@ __visible bool __kvm_vcpu_is_preempted(long cpu)
>  {
>  	struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>  
> -	return !!src->preempted;
> +	return !!(src->preempted & KVM_VCPU_PREEMPTED);
>  }
>  PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03869eb..5e63033 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2113,7 +2113,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>  		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
>  		return;
>  
> -	vcpu->arch.st.steal.preempted = 0;
> +	vcpu->arch.st.steal.preempted = KVM_VCPU_NOT_PREEMPTED;
>  
>  	if (vcpu->arch.st.steal.version & 1)
>  		vcpu->arch.st.steal.version += 1;  /* first time write, random junk */
> @@ -2884,7 +2884,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
>  	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
>  		return;
>  
> -	vcpu->arch.st.steal.preempted = 1;
> +	vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
>  
>  	kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,
>  			&vcpu->arch.st.steal.preempted,
> 


-- 

Thanks,

David / dhildenb