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Date: Fri, 21 Feb 2014 09:05:27 -0800
Message-ID: <CA+55aFwiHdFUnGRnYr_mXR0ga=exMiK0Xg8CcDXWyOWC7Vw9JQ@mail.gmail.com>
Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        George Spelvin <linux@horizon.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Daniel J Blueman <daniel@numascale.com>,
        Alexander Fyodorov <halcy@yandex.ru>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>,
        Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
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Sender: linux-kernel-owner@vger.kernel.org

On Fri, Feb 21, 2014 at 9:02 AM, Waiman Long <waiman.long@hp.com> wrote:
> On 02/20/2014 02:32 PM, Raghavendra K T wrote:
>>
>> On 02/20/2014 11:24 PM, Waiman Long wrote:
>>
>>> Now the key is how to detect if a kernel is really running in a PV
>>> environment. I need to ask some virtualization experts on that.
>>>
>>
>> For kvm you could just follow,
>> kvm_spinlock_init_jump() and KVM_FEATURE_* encoding in cpuid
>> part __do_cpuid_ent().
>>
>
> I saw that in the arch/x86/kernel/kvm.c file. So I think I can use the
> returned value of kvm_para_available() to decide if it is running in a KVM
> guest. However, I am not so sure of what to use in xen.

Just use that 'paravirt_ticketlocks_enabled' static key. Xen enables it too.

            Linus
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