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

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: linux-kernel@vger.kernel.org, vkuznets@redhat.com,
	linux-hyperv@vger.kernel.org, kvm@vger.kernel.org,
	Jonathan Corbet <corbet@lwn.net>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Sasha Levin <sashal@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 4/4] x86/hyperv: Mark "hv_nopvspin" parameter obsolete and map it to "nopvspin"
Date: Wed, 2 Oct 2019 10:19:52 -0700	[thread overview]
Message-ID: <20191002171952.GE9615@linux.intel.com> (raw)
In-Reply-To: <1569847479-13201-5-git-send-email-zhenzhong.duan@oracle.com>

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@oracle.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: "K. Y. Srinivasan" <kys@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Stephen Hemminger <sthemmin@microsoft.com>
> Cc: Sasha Levin <sashal@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.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
> 