linux-kernel - Re: [PATCHv3 1/1] locking/qspinlock/x86: Avoid test-and-set when PV

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Message-ID: <bbeaf134-b948-6ed4-d8a6-cdcb5279d1b3@redhat.com>
Date:   Fri, 10 Nov 2017 09:19:06 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, Radim Krcmar <rkrcmar@...hat.com>
Cc:     Eduardo Valentin <eduval@...zon.com>, Matt Wilson <msw@...zon.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>, kvm <kvm@...r.kernel.org>,
        linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jan H . Schoenherr" <jschoenh@...zon.de>,
        Anthony Liguori <aliguori@...zon.com>
Subject: Re: [PATCHv3 1/1] locking/qspinlock/x86: Avoid test-and-set when
 PV_DEDICATED is set

On 10/11/2017 07:07, Wanpeng Li wrote:
>>> You should also add a cpuid flag in kvm part.
>> It is better without that.  The flag has no dependency on KVM (kernel
>> hypervisor) code.
> Do you mean -cpu host, +xxxx，I think it will result in "warning: host
> doesn't support requested feature: CPUID.40000001H:eax.XXXXXX"

There are some exceptions where QEMU overrides the values of
KVM_GET_SUPPORTED_CPUID.

I think it is better to add the flag to KVM *and* to QEMU's override in
kvm_arch_get_supported_cpuid (target/i386/kvm.c).

Paolo