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] [PATCH] VT-d: improve RMRR validity checking, documentin

To: 'Pasi Kärkkäinen' <pasik@xxxxxx>, Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking, documenting boot options
From: Stephen Spector <stephen.spector@xxxxxxxxxx>
Date: Mon, 25 Jan 2010 11:40:53 -0500
Accept-language: en-US
Acceptlanguage: en-US
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>, Weidong Han <weidong.han@xxxxxxxxx>, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Delivery-date: Mon, 25 Jan 2010 08:41:12 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <20100123145435.GO2861@xxxxxxxxxxx>
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: <4B590FA4.4000008@xxxxxxxxxxxxxx> <4B59132B.40607@xxxxxxxxx> <4B59188C.50901@xxxxxxxxxxxxxx> <4B59660F.4000909@xxxxxxxxx> <1098023846.20100122101901@xxxxxxxxxxxxxx> <4B5996CF.9020409@xxxxxxxxx> <20100122123235.GZ2861@xxxxxxxxxxx> <4B5AEE2A.5040100@xxxxxxxxx> <20100123130850.GJ2861@xxxxxxxxxxx> <466427676.20100123153350@xxxxxxxxxxxxxx> <20100123145435.GO2861@xxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcqcO/xe1hjHYAaYS8WkQ08citebQABoLJ5A
Thread-topic: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking, documenting boot options

The document in question is located at 
http://www.xen.org/files/Support/XenConfigurationDetails.pdf. I am going to 
move the document into the Xen Wiki this morning and will have the final 
version at http://wiki.xensource.com/xenwiki/XenConfigurationFileOptions. 


-----Original Message-----
From: Pasi Kärkkäinen [mailto:pasik@xxxxxx] 
Sent: Saturday, January 23, 2010 9:55 AM
To: Sander Eikelenboom
Cc: Weidong Han; xen-devel@xxxxxxxxxxxxxxxxxxx; Kay, Allen M; Cihula, Joseph; 
Noboru Iwamatsu; Keir Fraser; Stephen Spector
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking, 
documenting boot options

On Sat, Jan 23, 2010 at 03:33:50PM +0100, Sander Eikelenboom wrote:
> Hmm perhaps somewhat unrelated, but is there a comprehensive list with Xen 
> specific boot options with explanation ?
> Since some seem to be valid for some for pvops as well, and the 
> hypervisor has some of her own.
> If not I could perhaps try to make a Wiki with a table with options and 
> explanation for it ?
> This discussion seems to show sometimes you can interpret some option names 
> in multiple ways and things have additional consequences.

Have you checked this wiki page?:

But yeah, I think we should definitely add a wiki page
describing all the Xen + Dom0 kernel options.. a list that's up to date.

Stephen: Did you make some PDF document about Xen hypervisor boot options? 
I remember you doing PDF about the /etc/xen/<guest> cfgfile options earlier.

I think these documents should be put to a wiki page, it's much easier to update
and read them there.

-- Pasi

> --
> Sander
> Saturday, January 23, 2010, 2:08:50 PM, you wrote:
> > On Sat, Jan 23, 2010 at 08:40:10PM +0800, Weidong Han wrote:
> >> Pasi Kärkkäinen wrote:
> >>> On Fri, Jan 22, 2010 at 08:15:11PM +0800, Weidong Han wrote:
> >>>   
> >>>> Sander Eikelenboom wrote:
> >>>>     
> >>>>> Hello Weidong,
> >>>>>
> >>>>> Wouldn't it be more clear to add an option to iommu= for this case ?
> >>>>>
> >>>>> if iommu=on,..,..,security
> >>>>>
> >>>>> With the security option specified:
> >>>>>      -it would be most strict in it's checks, since enforcing security 
> >>>>> with the iommu requires that as you have pointed out.
> >>>>>      -warn,fail or panic incase it can't enable all to enforce the 
> >>>>> security.
> >>>>>         
> >>>> iommu=force is for security. It does as you described above. So I 
> >>>> think  "security" option is not necessary.
> >>>>     
> >>>>> Without the security option specified (default)
> >>>>>      - it tries to work as with the security option specified
> >>>>>      - but incase of problems makes the assumption the iommu's main 
> >>>>> task is not security, but making as much of vt-d working to keep the 
> >>>>> passthrough functionality
> >>>>>      - it will only warn, that you will lose the security part, that it 
> >>>>> would be wise to let your bios be fixed, and not making it panic
> >>>>>      - and keep vt-d enabled
> >>>>>
> >>>>>         
> >>>> the default iommu=1 works like iommu=force if BIOS is correct. But in 
> >>>>  fact we encountered some buggy BIOS, and then we added some 
> >>>> workarounds  to make VT-d still be enabled,  or warn and disable VT-d 
> >>>> if the issue is  regarded as invalid and cannot be workarounded. 
> >>>> These workarounds make  Xen more defensive to VT-d BIOS issues. The 
> >>>> panic only occurs when  operating VT-d hardware fails, because it 
> >>>> means the hardware is possibly  malfunctional.
> >>>>
> >>>> In short, default iommu=1 can workaround known VT-d BIOS issues we   
> >>>> observed till now, while iommu=force ensures best security provided 
> >>>> by VT-d.
> >>>>
> >>>>     
> >>>
> >>> So the default iommu=1 might be insecure? And iommu=force is always 
> >>> secure? 
> >>>
> >>> To me "force" sounds like it makes it work always, no matter if it's 
> >>> secure or not..
> >>>   
> >> The "security" here means the protection provided VT-d. The main  
> >> difference between them is iommu=force tries to enable all VT-d units in  
> >> any case, if any VT-d unit cannot enabled, it will quit Xen booting  
> >> (panic), thus it guarantees security provided by VT-d. while when  
> >> iommu=1, in order to workaround some BIOS issues, it will ignore some  
> >> invalid DRHDs, or disable whole VT-d to keep Xen work without VT-d. 
> >>
> > Ok.. Thanks for explaining it. 
> > -- Pasi
> -- 
> Best regards,
>  Sander                            mailto:linux@xxxxxxxxxxxxxx

Xen-devel mailing list

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