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] Some things to be considered for ptc.ga emulation

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-ia64-devel] Some things to be considered for ptc.ga emulation
From: Tristan Gingold <Tristan.Gingold@xxxxxxxx>
Date: Fri, 7 Apr 2006 08:35:11 +0100
Delivery-date: Fri, 07 Apr 2006 00:31:28 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <571ACEFD467F7749BC50E0A98C17CDD8094E7AB3@pdsmsx403>
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>
References: <571ACEFD467F7749BC50E0A98C17CDD8094E7AB3@pdsmsx403>
Sender: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: KMail/1.5
Le Vendredi 07 Avril 2006 09:18, Tian, Kevin a écrit :
> From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
>
> >Sent: 2006年4月7日 15:04
> >
> >> Sorry for my question, but I really can't convince myself such
> >> code immune from race. :-) It's possible another side to clear
> >> present bit of current dtlb right after pass of above check. In
> >> that case, the TC entry is still inserted into TLB. Since the logic
> >> can't prevent all the cases, that check seems excessive here.
> >
> >I don't agree.  If a vcpu_ptc_ga clears dtlb after this, it will also
> > execute the ptc.ga.
>
> Yes, this answers my concern...
Ok.

> >> >- if (/* is_data && */ vcpu_match_tr_entry(trp,address,rid)) {
> >> >-         if (vcpu->domain==dom0 && !in_tpa) *pteval =
> >> >trp->page_flags;
> >> >+ pte = trp->pte;
> >> >+ if (/* is_data && */ pte.p
> >> >+     && vcpu_match_tr_entry_no_p(trp,address,rid)) {
> >>
> >> Above change seems no difference as original code.
> >
> >It uses _no_p.
> >The aim is to read pags_flags once!
>
> If you use vcpu_match_tr_entry here, you still only read page_flags
> once, see below:
> +static inline int vcpu_match_tr_entry(TR_ENTRY *trp, UINT64 ifa, UINT64
> rid) +{
> +     return trp->pte.p && vcpu_match_tr_entry_no_p(trp, ifa, rid);
> +}
>
> I think at assembly level, trp->pte.p is expanded same as
> "pte=trp->pte; pte.p"
No.  pte is volatile.

> >> Concerns here:
> >>    - The per-LP vhpt table is shared by all domains, and the entry
> >> sitting at the hash position may not belong to target domain. By above
> >> way, you may finally purge unrelated entry of other domain. So check
> >> upon tag value is required
> >
> >Yes.  Call this an optimization.
>
> Just in case there's corner case though I didn't came up one. :-(
>
> >>    - When hash tlb is added with collision chain support, this remote
> >> purge is more dangerous since there'll be link list operation which
> >> however has no lock protection.
> >
> >Hash tlb requires more analysis.
>
> Hope the interface to be unique irregardless of whether hash or not.
>
> >> Last point, so far your patch only aims for vtlb and vhpt. Machine
> >> TLB purge is not covered yet which however is the most direct place
> >> required to be handled. :-)
> >
> >I don't understand.
> >vcpu_ptc_ga still calls      ia64_global_tlb_purge, which does ptc.ga
>
> My fault, since I only looked at your patch where no existence of
> global_tlb_purge (it's in original code).
>
> So, no more questions from me by far.
Ok.

Tristan.


_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel

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