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/
Home Products Support Community News


RE: [Xen-devel] Regarding page table management changes from Xen v1to Xe

To: "Himanshu Raj" <rhim@xxxxxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] Regarding page table management changes from Xen v1to Xen v2 (and v3)
From: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Date: Wed, 26 Apr 2006 13:49:15 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Wed, 26 Apr 2006 13:49:33 -0700
Envelope-to: www-data@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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcZpYqouhwQ+RvoMTniex/yEHBROvwACVDQA
Thread-topic: [Xen-devel] Regarding page table management changes from Xen v1to Xen v2 (and v3)
Himanshu Raj wrote:
>>> Could you tell me another example other than fork when one can use
>>> batched PTE modifications.
>> fork() is the only one for us these days. All others use
>> update_va_mapping(), act on pagetables that aren't pinned (so the
>> guest can directly update them without faulting) or are infrequent
>> enough we do not care.
> Not sure I understand the last part (aren't pinned ...) - my
> assumptions about 
> page tables are (these apply to both direct mapped and shadow page
> tables): 
> 1. Always pinned (backed) - so a access to them cannot cause a page
> unavailable fault. 
> 2. Always read only to guest - so a read access to them is fine, but
>    a write access will cause a protection fault.

Today we pin once per page table when the root is pinned (rather than
any of the other levels). So whatever page tables populated later, for
example, are not pinned (they have been a data page). 

> Both of these faults are reflected as a PG fault.
> Are you refering to the case when Xen has "detached" the page table
> page and 
> has made it RW for guest?
> Thanks for your answers and patience :-).
> -Himanshu

Intel Open Source Technology Center

Xen-devel mailing list