linux-kernel - Re: [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS

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Date:   Thu, 17 May 2018 18:05:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS_REALTIME

On 17/05/2018 16:54, Michael S. Tsirkin wrote:
> HINTS_DEDICATED seems to be somewhat confusing:
> 
> Guest doesn't really care whether it's the only task running on a host
> CPU as long as it's not preempted.
> 
> And there are more reasons for Guest to be preempted than host CPU
> sharing, for example, with memory overcommit it can get preempted on a
> memory access, post copy migration can cause preemption, etc.
> 
> Let's call it KVM_HINTS_REALTIME which seems to better
> match what guests expect.
> 
> Also, the flag most be set on all vCPUs - current guests assume this.
> Note so in the documentation.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  Documentation/virtual/kvm/cpuid.txt  | 6 +++---
>  arch/x86/include/uapi/asm/kvm_para.h | 2 +-
>  arch/x86/kernel/kvm.c                | 8 ++++----
>  3 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index d4f33eb8..ab022dc 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -72,8 +72,8 @@ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
>  
>  flag                               || value || meaning
>  ==================================================================================
> -KVM_HINTS_DEDICATED                ||     0 || guest checks this feature bit to
> -                                   ||       || determine if there is vCPU pinning
> -                                   ||       || and there is no vCPU over-commitment,
> +KVM_HINTS_REALTIME                 ||     0 || guest checks this feature bit to
> +                                   ||       || determine that vCPUs are never
> +                                   ||       || preempted for an unlimited time,
>                                     ||       || allowing optimizations
>  ----------------------------------------------------------------------------------
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 4c851eb..0ede697 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -29,7 +29,7 @@
>  #define KVM_FEATURE_PV_TLB_FLUSH	9
>  #define KVM_FEATURE_ASYNC_PF_VMEXIT	10
>  
> -#define KVM_HINTS_DEDICATED      0
> +#define KVM_HINTS_REALTIME      0
>  
>  /* The last 8 bits are used to indicate how to interpret the flags field
>   * in pvclock structure. If no bits are set, all flags are ignored.
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 7867417..5b2300b 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -457,7 +457,7 @@ static void __init sev_map_percpu_data(void)
>  static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)
>  {
>  	native_smp_prepare_cpus(max_cpus);
> -	if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
> +	if (kvm_para_has_hint(KVM_HINTS_REALTIME))
>  		static_branch_disable(&virt_spin_lock_key);
>  }
>  
> @@ -553,7 +553,7 @@ static void __init kvm_guest_init(void)
>  	}
>  
>  	if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> -	    !kvm_para_has_hint(KVM_HINTS_DEDICATED) &&
> +	    !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
>  	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
>  		pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;
>  
> @@ -649,7 +649,7 @@ static __init int kvm_setup_pv_tlb_flush(void)
>  	int cpu;
>  
>  	if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> -	    !kvm_para_has_hint(KVM_HINTS_DEDICATED) &&
> +	    !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
>  	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
>  		for_each_possible_cpu(cpu) {
>  			zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu),
> @@ -745,7 +745,7 @@ void __init kvm_spinlock_init(void)
>  	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
>  		return;
>  
> -	if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
> +	if (kvm_para_has_hint(KVM_HINTS_REALTIME))
>  		return;
>  
>  	__pv_init_lock_hash();
> 

Queued, thanks.

Paolo