linux-kernel - Re: [PATCH v3 4/4] x86/hyperv: Mark "hv_nopvspin" parameter obsolete and map it to "nopvspin"

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Date:   Wed, 2 Oct 2019 10:19:52 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:     linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        linux-hyperv@...r.kernel.org, kvm@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 4/4] x86/hyperv: Mark "hv_nopvspin" parameter obsolete
 and map it to "nopvspin"

On Mon, Sep 30, 2019 at 08:44:39PM +0800, Zhenzhong Duan wrote:
> Includes asm/hypervisor.h in order to reference x86_hyper_type.
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: Sasha Levin <sashal@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
>  arch/x86/hyperv/hv_spinlock.c                   | 9 +++++----
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1f0a62f..43f922c 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1436,6 +1436,10 @@
>  	hv_nopvspin	[X86,HYPER_V] Disables the paravirt spinlock optimizations
>  				      which allow the hypervisor to 'idle' the
>  				      guest on lock contention.
> +				      This parameter is obsoleted by "nopvspin"
> +				      parameter, which has equivalent effect for
> +				      HYPER_V platform.
> +
>  
>  	keep_bootcon	[KNL]
>  			Do not unregister boot console at start. This is only
> @@ -5331,7 +5335,7 @@
>  			as generic guest with no PV drivers. Currently support
>  			XEN HVM, KVM, HYPER_V and VMWARE guest.
>  
> -	nopvspin	[X86,XEN,KVM] Disables the qspinlock slow path
> +	nopvspin	[X86,XEN,KVM,HYPER_V] Disables the qspinlock slow path
>  			using PV optimizations which allow the hypervisor to
>  			'idle' the guest on lock contention.
>  
> diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
> index 07f21a0..e00e319 100644
> --- a/arch/x86/hyperv/hv_spinlock.c
> +++ b/arch/x86/hyperv/hv_spinlock.c
> @@ -12,12 +12,11 @@
>  
>  #include <linux/spinlock.h>
>  
> +#include <asm/hypervisor.h>
>  #include <asm/mshyperv.h>
>  #include <asm/paravirt.h>
>  #include <asm/apic.h>
>  
> -static bool __initdata hv_pvspin = true;
> -
>  static void hv_qlock_kick(int cpu)
>  {
>  	apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR);
> @@ -64,7 +63,7 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
>  
>  void __init hv_init_spinlocks(void)
>  {
> -	if (!hv_pvspin || !apic ||
> +	if (!pvspin || !apic ||
>  	    !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
>  	    !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {
>  		pr_info("PV spinlocks disabled\n");
> @@ -82,7 +81,9 @@ void __init hv_init_spinlocks(void)
>  
>  static __init int hv_parse_nopvspin(char *arg)
>  {
> -	hv_pvspin = false;
> +	pr_notice("\"hv_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
> +	if (x86_hyper_type == X86_HYPER_MS_HYPERV)
> +		pvspin = false;

Personal preference would be to keep the hv_pvspin variable and add the
extra check in hv_init_spinlocks().

>  	return 0;
>  }
>  early_param("hv_nopvspin", hv_parse_nopvspin);
> -- 
> 1.8.3.1
>