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Subject: Re: [PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the
 hv_nopvspin case
To:     linux-kernel@vger.kernel.org
Cc:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sasha Levin <sashal@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Waiman Long <longman@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        linux-hyperv@vger.kernel.org
References: <1562120635-9806-1-git-send-email-zhenzhong.duan@oracle.com>
From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
Organization: Oracle Corporation
Message-ID: <a3b87a0e-803d-5a28-03be-b9e2b37b94ba@oracle.com>
Date:   Wed, 24 Jul 2019 15:29:05 +0800
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Hi Maintainers,

Any further comments on this? Thanks

Zhenzhong

On 2019/7/3 10:23, Zhenzhong Duan wrote:
> With the boot parameter "hv_nopvspin" specified a Hyperv guest should
> not make use of paravirt spinlocks, but behave as if running on bare
> metal. This is not true, however, as the qspinlock code will fall back
> to a test-and-set scheme when it is detecting a hypervisor.
>
> In order to avoid this disable the virt_spin_lock_key.
>
> Same change for XEN is already in Commit e6fd28eb3522
> ("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> 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: Juergen Gross <jgross@suse.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: linux-hyperv@vger.kernel.org
> ---
> v3: remove unlikely() as suggested by Sasha
>
>   arch/x86/hyperv/hv_spinlock.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
> index 07f21a0..210495b 100644
> --- a/arch/x86/hyperv/hv_spinlock.c
> +++ b/arch/x86/hyperv/hv_spinlock.c
> @@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
>   
>   void __init hv_init_spinlocks(void)
>   {
> +	if (!hv_pvspin)
> +		static_branch_disable(&virt_spin_lock_key);
> +
>   	if (!hv_pvspin || !apic ||
>   	    !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
>   	    !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {