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-ia64-devel

RE: [Xen-ia64-devel] flush.S not para-virtualized

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, "Tristan Gingold" <Tristan.Gingold@xxxxxxxx>, <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-ia64-devel] flush.S not para-virtualized
From: "Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>
Date: Mon, 27 Mar 2006 09:16:46 -0800
Delivery-date: Mon, 27 Mar 2006 17:18:05 +0000
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
List-help: <mailto:xen-ia64-devel-request@lists.xensource.com?subject=help>
List-id: Discussion of the ia64 port of Xen <xen-ia64-devel.lists.xensource.com>
List-post: <mailto:xen-ia64-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-ia64-devel>, <mailto:xen-ia64-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-ia64-devel>, <mailto:xen-ia64-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcZRtghNXvTVtyPQQIKbrcDqQ5EIiwAASDegAAKeP2A=
Thread-topic: [Xen-ia64-devel] flush.S not para-virtualized
Hmmm... Kevin, you may be right.  My memory is dim on this
(as it was >15 months ago), but at some point an fc instruction
in linux did cause an unexpected trap.  This was back when
I was still working with a privified kernel, probably older
than 2.6.9.  IIRC, the problem occurred during one of the
patches in linux/arch/ia64/kernel/patch.c.

It's possible that this was due to a bug, or it may have
been dealing with an epc page.

Dan

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx] 
> Sent: Monday, March 27, 2006 9:16 AM
> To: Tristan Gingold; Magenheimer, Dan (HP Labs Fort Collins); 
> xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-ia64-devel] flush.S not para-virtualized
> 
> >From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
> >Sent: 2006年3月27日 23:52
> >
> >Le Lundi 27 Mars 2006 17:24, Magenheimer, Dan (HP Labs Fort Collins)
> >a écrit :
> >> Agreed, this needs to be paravirtualized.
> >So, everybody agree.
> >I will add a fc.i hyperprivop.
> >
> >However, I fear the hyperprivop-ized version of flush.S would be very
> >slow.
> >Should we also create an hyperprivop for something like
> >flush_icache_range ?
> >
> >Tristan.
> 
> Normally more thinking brings more questions. :-) SDM says:
> 
> When executed at privilege level 0, fc and fc.i perform no 
> access rights or 
> protection key checks. At other privilege levels, fc and fc.i 
> perform access 
> rights checks as if they were 1-byte reads, but do not perform any 
> protection key checks (regardless of PSR.pk).
> 
> Easy to see hint here to protect memory pages of higher 
> region can't be 
> affected by lower privilege level, or else the performance 
> may be affected 
> a lot by malicious programs. Then let's see which cases 1-byte reads 
> can't pass access rights checks in current environment:
> 
> First we have TLB.pl == 2, and xenlinux kernel also executes 
> at cpl==2. In 
> all 8 types of access rights, 0-6 all support read at same 
> privilege level 
> with only exception as type 7 (execute,promote/read,execute). However 
> that page is special to contain 'epc' instruction. Content on 
> that page is 
> normally fixed and stable, and it's difficult to find good 
> reason to flush 
> cache entry for that page.
> 
> If it's true with only one weak exception, is it really 
> worthy of virtualizing 
> fc.i? :-)
> 
> Thanks,
> Kevin
> 
_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel