linux-kernel - Re: [PATCH 1/3] KVM: X86: Add "nopvspin" parameter to disable PV spinlocks

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Message-ID: <87eezw3lna.fsf@vitty.brq.redhat.com>
Date:   Tue, 01 Oct 2019 10:39:05 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        linux-kernel@...r.kernel.org
Cc:     Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/3] KVM: X86: Add "nopvspin" parameter to disable PV spinlocks

Zhenzhong Duan <zhenzhong.duan@...cle.com> writes:

> On 2019/9/30 23:41, Vitaly Kuznetsov wrote:
>> Zhenzhong Duan<zhenzhong.duan@...cle.com>  writes:
>>
>>> There are cases where a guest tries to switch spinlocks to bare metal
>>> behavior (e.g. by setting "xen_nopvspin" on XEN platform and
>>> "hv_nopvspin" on HYPER_V).
>>>
>>> That feature is missed on KVM, add a new parameter "nopvspin" to disable
>>> PV spinlocks for KVM guest.
>>>
>>> This new parameter is also intended to replace "xen_nopvspin" and
>>> "hv_nopvspin" in the future.
>> Any reason to not do it right now? We will probably need to have compat
>> code to support xen_nopvspin/hv_nopvspin too but emit a 'is deprecated'
>> warning.
>
> Sorry the description isn't clear, I'll fix it.
>
> I did the compat work in the other two patches.
> [PATCH 2/3] xen: Mark "xen_nopvspin" parameter obsolete and map it to "nopvspin"
> [PATCH 3/3] x86/hyperv: Mark "hv_nopvspin" parameter obsolete and map it to "nopvspin"
>

For some reason I got CCed only on the first one and moreover, I don't
see e.g PATCH3 on 'linux-hyperv' mailing list.

>>
>>> The global variable pvspin isn't defined as __initdata as it's used at
>>> runtime by XEN guest.
>>>
>>> Refactor the print stuff with pr_* which is preferred.
>> Please do it in a separate patch.
>
> Ok, I'll do that in v2. Thanks for review.

Thanks!

-- 
Vitaly