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Subject: Re: [PATCH v4 13/17] kvm: i8254: Deactivate APICv when using
 in-kernel PIT re-injection mode.
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
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        "Grimm, Jon" <Jon.Grimm@amd.com>
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 <1572648072-84536-14-git-send-email-suravee.suthikulpanit@amd.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Sat, 2 Nov 2019 10:57:47 +0100
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On 01/11/19 23:41, Suthikulpanit, Suravee wrote:
> +	/*
> +	 * AMD SVM AVIC accelerates EOI write and does not trap.
> +	 * This cause in-kernel PIT re-inject mode to fail
> +	 * since it checks ps->irq_ack before kvm_set_irq()
> +	 * and relies on the ack notifier to timely queue
> +	 * the pt->worker work iterm and reinject the missed tick.
> +	 * So, deactivate APICv when PIT is in reinject mode.
> +	 */
>  	if (reinject) {
> +		kvm_request_apicv_update(kvm, false, APICV_DEACT_BIT_PIT_REINJ);
>  		/* The initial state is preserved while ps->reinject == 0. */
>  		kvm_pit_reset_reinject(pit);
>  		kvm_register_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
>  		kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
>  	} else {
> +		kvm_request_apicv_update(kvm, true, APICV_DEACT_BIT_PIT_REINJ);
>  		kvm_unregister_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
>  		kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);

This is not too nice for Intel which does support (through the EOI exit
mask) APICv even if PIT reinjection active.

We can work around it by adding a global mask of inhibit reasons that
apply to the vendor, and initializing it as soon as possible in vmx.c/svm.c.

Then kvm_request_apicv_update can ignore reasons that the vendor doesn't
care about.

Paolo