Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking

[Weidong Han <weidong.han@xxxxxxxxx>]

Noboru Iwamatsu wrote:
> Hi,
>
> After registered invalid DRHDs, Xen hangs in boot time.
>   
Can you post the logs?

Regards,
Weidong
> About RMRR, I understood the logic.
> In my mainboard, unfortunately, RMRR has non-existent device under
> its scope, and to make matters worse, the RMRR range is invalid.
> So, I think RMRR that has no-existent device is valid.
>
> How do you think about these?
>
>   
> > Hi Noboru,
> >
> > You should not ignore DRHD even if devices under its scope are not pci discoverable. For 
> > the sake of security, we still enable these DRHDs but don't set any context mappings. In 
> > that case, any DMA that comes from these "supposedly disabled" devices will get 
> > blocked by VT-d, and hence avoid any security vulnerability with malicious s/w 
> > re-enabling these devices.
> >
> > You RMRR validity fixing is wrong. My RMRR patch is no problem. Pls note that 
> > the RMRR checking logic is:
> >         If all devices under RMRR's scope are not pci discoverable
> >                 Ignore the RMRR
> >         Else if base_address>  end_address
> >                 Return error
> >         Else
> >                 Register RMRR
> >
> > Regards,
> > Weidong
> >                 
> >
> > -----Original Message-----
> > From: Noboru Iwamatsu [mailto:n_iwamatsu@xxxxxxxxxxxxxx]
> > Sent: Thursday, January 21, 2010 4:26 PM
> > To: Han, Weidong
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; keir.fraser@xxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
> >
> > Hi,
> >
> > Some Q35 mainboard that has buggy BIOS, I have one of this, reports invalid 
> > DRHD in addition to the invalid RMRR.
> >
> > Attached patch fixes this DRHD issue in the same way as RMRR.
> > And also, I fixed RMRR validity checking loop.
> >
> > Noboru.
> >
> > Signed-off-by: Noboru Iwamatsu<n_iwamatsu@xxxxxxxxxxxxxx>
> >
> >
> > -------- Original Message  --------
> > Subject: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
> > From: Han, Weidong<weidong.han@xxxxxxxxx>
> > To: xen-devel@xxxxxxxxxxxxxxxxxxx<xen-devel@xxxxxxxxxxxxxxxxxxx>
> > Date: Thu Jan 21 2010 11:46:12 GMT+0900
> >
> >     
> > > Currently, Xen checks RMRR range and disables VT-d if RMRR range is set 
> > > incorrectly in BIOS rigorously. But, actually we can ignore the RMRR if the 
> > > device under its scope are not pci discoverable, because the RMRR won't be used 
> > > by non-existed or disabled devices.
> > >
> > > This patch ignores the RMRR if the device under its scope are not pci 
> > > discoverable, and only checks the validity of RMRRs that are actually used. In 
> > > order to avoid duplicate pci device detection code, this patch defines a 
> > > function pci_device_detect for it.
> > >
> > > Signed-off-by: Weidong Han<weidong.han@xxxxxxxxx>
> > >
> > >
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> > >       
>
>   

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