linux-kernel - Re: [PATCH v2 10/15] kvm: x86: hyperv: Use APICv deactivate request interface

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Message-ID: <2b26daff-6970-cca4-8553-962a6d829bdd@amazon.com>
Date:   Mon, 19 Aug 2019 12:31:24 +0200
From:   Alexander Graf <graf@...zon.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:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "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 v2 10/15] kvm: x86: hyperv: Use APICv deactivate request
 interface



On 15.08.19 18:25, Suthikulpanit, Suravee wrote:
> Since disabling APICv has to be done for all vcpus on AMD-based system,
> adopt the newly introduced kvm_make_apicv_deactivate_request() intereface.

typo

> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>   arch/x86/kvm/hyperv.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index a39e38f..4f71a39 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -772,9 +772,17 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
>   
>   	/*
>   	 * Hyper-V SynIC auto EOI SINT's are
> -	 * not compatible with APICV, so deactivate APICV
> +	 * not compatible with APICV, so  request

double space

> +	 * to deactivate APICV permanently.
> +	 *
> +	 * Since this requires updating
> +	 * APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
> +	 * also take srcu lock.
>   	 */
> -	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);

Overall, I'm not terribly happy with the srcu locks. Can't we handle the 
memslot changes outside of the lock region, inside the respective 
request handlers somehow?


Alex

> +
>   	synic->active = true;
>   	synic->dont_zero_synic_pages = dont_zero_synic_pages;
>   	return 0;
>