From: Jeremy Fitzhardinge <jeremy@goop.org>
To: "Jiang, Yunhong" <yunhong.jiang@intel.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: One question on xen_cpuid in pv guest
Date: Thu, 30 Jul 2009 10:06:36 -0700 [thread overview]
Message-ID: <4A71D31C.7020307@goop.org> (raw)
In-Reply-To: <E2263E4A5B2284449EEBD0AAB751098402CDF659F0@PDSMSX501.ccr.corp.intel.com>
On 07/29/09 22:44, Jiang, Yunhong wrote:
> Jeremy, thanks for clarification, but I still not sure about following code in pv_ops dom0. Since the Local APIC is owned by Xen totally, why is it not "outright forbidden for the guest"?
>
>
> if (!xen_initial_domain())
> cpuid_leaf1_edx_mask &=
> ~((1 << X86_FEATURE_APIC) | /* disable local APIC */
> (1 << X86_FEATURE_ACPI)); /* disable ACPI */
>
Some of the approaches to implementing dom0 pretend the local APIC
exists in order to fool various code-paths into doing the right thing
(for example, getting the kernel to parse all the MADT tables, which it
won't do if there's no local APIC).
Historically I think the policy has been for Xen to explicitly blacklist
features which turn out to be problematic when they become problematic,
rather than whitelist features known to be safe.
J
prev parent reply other threads:[~2009-07-30 17:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-29 3:19 One question on xen_cpuid in pv guest Jiang, Yunhong
2009-07-29 16:54 ` Jeremy Fitzhardinge
2009-07-30 5:44 ` Jiang, Yunhong
2009-07-30 17:06 ` Jeremy Fitzhardinge [this message]
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