WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] APIC MSRs query

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] APIC MSRs query
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date: Tue, 17 May 2011 14:49:50 +0100
Cc: xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Tue, 17 May 2011 06:50:31 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4DD297B90200007800041A32@xxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <4DD27760.9020706@xxxxxxxxxx> <4DD297B90200007800041A32@xxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10


On 17/05/11 14:43, Jan Beulich wrote:
On 17.05.11 at 15:25, Andrew Cooper<andrew.cooper3@xxxxxxxxxx>  wrote:
Hello,

I am currently cleaning up the APIC code for the sake of
shutdown/reboot/crashdump and have a query about the (modified for
brevity) snippet of code:

uint64_t msr_content;
rdmsrl(MSR_IA32_APICBASE, msr_content);
msr_content |= MSR_IA32_APICBASE_ENABLE | MSR_IA32_APICBASE_EXTD;
msr_content = (uint32_t)msr_content;
wrmsrl(MSR_IA32_APICBASE, msr_content);

which is added into apic.c in changeset b622e411eef8, and has propagated
elsewhere in the codebase during subsequent cleanups etc.

The MP spec and x2apic spec states that bits [35:12] of
MSR_IA32_APICBASE is the base APIC MMIO address.  Is there reason why
the code (almost always) clears the top 4 bits, or is it just an
overlooked mistake?
I think this is a benign mistake. Benign because I don't think there is
a meaningful (to Xen at least) number of systems that would not
have their LAPIC at the default address (which fits in 32 bits).

Jan

Ok - I will fix this up in my cleanup.

--
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>