linux-kernel - Re: [PATCH] xen: HVM X2APIC support

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Message-ID: <alpine.DEB.2.00.1012031119270.14723@kaball-desktop>
Date:	Fri, 3 Dec 2010 11:29:40 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Sheng Yang <sheng@...ux.intel.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	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] xen: HVM X2APIC support

On Fri, 3 Dec 2010, Sheng Yang wrote:
> I suppose only HVM guest without XENFEAT_hvm_pirqs may need this. But does this 
> code covered PV guest as well? We don't need cover them.
> 

We can add a check on xen_pv_domain() to rule PV guests out.

> > }
> > #else
> > static inline bool xen_para_available(void)
> > {
> > 	return (xen_cpuid_base() != 0);
> > }
> > #endif
> > 
> > 
> > This is assuming that enabling x2apic doesn't prevent Linux from
> > receiving evtchns either using the callback vector mechanism or the
> > legacy platform-pci interrupt.
> 
> I suppose only legacy platform-pci would need this, because it would use lapic. 
> Callback vector method would use evtchn so this won't be enabled.
> 

Right, should add a check on xen_have_vector_callback too.


> > Finally when running as dom0 would this feature create problems in the
> > presence of a real x2apic?
> 
> I don't think this can be enabled on dom0.
> 
> This one target on HVM domain, maybe also PVHVM domain without XENFEAT_hvm_pirqs, 
> but not the domains using evtchn.
> 

Ok, a check on xen_pv_domain() will disable x2apic for both pv guests
and dom0:


#ifdef CONFIG_XEN_PVHVM
static inline bool xen_para_available(void)
{
    if (xen_pv_domain())
        return 0;
    if (xen_cpuid_base() != 0 &&
            xen_feature(XENFEAT_hvm_pirqs) &&
            xen_have_vector_callback)
        return 0;
    else
        return 1;
}

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