linux-kernel - Re: [PATCH v3 09/16] kvm: x86: hyperv: Use APICv deactivate request interface

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Message-ID: <449c5ea4-9353-1822-10e6-7b10f5a1a6f3@redhat.com>
Date:   Wed, 9 Oct 2019 11:21:50 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "graf@...zon.com" <graf@...zon.com>,
        "jschoenh@...zon.de" <jschoenh@...zon.de>,
        "karahmed@...zon.de" <karahmed@...zon.de>,
        "rimasluk@...zon.com" <rimasluk@...zon.com>,
        "Grimm, Jon" <Jon.Grimm@....com>
Subject: Re: [PATCH v3 09/16] kvm: x86: hyperv: Use APICv deactivate request
 interface

On 13/09/19 21:01, Suthikulpanit, Suravee wrote:
> +	 *
> +	 * Since this requires updating
> +	 * APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
> +	 * also take srcu lock.

This comment is incorrect, it says you are entering a read-side critical
section to update the data structure.  It's only needed because
kvm_make_apicv_deactivate_request expects that it needs to unlock and
relock kvm->srcu.

Paolo

>  	 */
> -	kvm_vcpu_deactivate_apicv(vcpu);
> +	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> +	kvm_make_apicv_deactivate_request(vcpu, true);
> +	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> +