linux-kernel - Re: [PATCH 5/7] xen: Make event channel work with PV featured HVM

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Message-ID: <1265716376.24394.32669.camel@zakaz.uk.xensource.com>
Date:	Tue, 9 Feb 2010 11:52:56 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Sheng Yang <sheng@...ux.intel.com>
CC:	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Keir Fraser <Keir.Fraser@...citrix.com>,
	xen-devel <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] xen: Make event channel work with PV featured HVM

On Mon, 2010-02-08 at 08:05 +0000, Sheng Yang wrote:
> +       if (xen_hvm_pv_evtchn_enabled()) {
> +               if (enable_hvm_pv(HVM_PV_EVTCHN))
> +                       return -EINVAL;
> +[...]
> +               callback_via = HVM_CALLBACK_VECTOR(X86_PLATFORM_IPI_VECTOR);
> +               set_callback_via(callback_via);
> +
> +               x86_platform_ipi_callback = do_hvm_pv_evtchn_intr; 

Why this indirection via X86_PLATFORM_IPI_VECTOR?

Apart from that why not use CALLBACKOP_register subop CALLBACKTYPE_event
pointing to xen_hypervisor_callback the same as a full PV guest?

This would remove all the evtchn related code from HVMOP_enable_pv which
I think should be eventually unnecessary as an independent hypercall
since all HVM guests should simply be PV capable by default -- the
hypervisor only needs to track if the guest has made use of specific PV
functionality, not the umbrella "is PV" state.

Ian.

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