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

[Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>]

Hi,

After registered invalid DRHDs, Xen hangs in boot time.

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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