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

[Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>]

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@jp.fujitsu.com]
> Sent: Thursday, January 21, 2010 4:26 PM
> To: Han, Weidong
> Cc: xen-devel@lists.xensource.com; keir.fraser@eu.citrix.com
> 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@jp.fujitsu.com>
>
>
> -------- Original Message  --------
> Subject: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
> From: Han, Weidong<weidong.han@intel.com>
> To: xen-devel@lists.xensource.com<xen-devel@lists.xensource.com>
> 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@intel.com>
>>
>>
>>
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>