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

Andrew Lyon wrote:
On Thu, Jan 21, 2010 at 8:25 AM, Noboru Iwamatsu
<n_iwamatsu@xxxxxxxxxxxxxx> wrote:
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>



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I have a Supermicro X7DWA-N system which requires
iommu_inclusive_mapping=1 in order to boot Xen successfully with iommu
enabled, I am going to try these patches to see if the workaround is
still necessary but I would also like to ask for some help in getting
the bios fixed properly , I contacted Supermicro about this issue last
year and they said they would fix it but they wanted details of
exactly what was wrong, I tried to figure it out by using acpidump and
reading the rmrr spec but I failed to make sense of it, perhaps you
could have a quick look at this dump and let me know if there is
anything obviously wrong?

iommu_inclusive_mapping=1 workarounds another problem. These code in Xen just 
makes Xen more defensive to BIOS errors. The final solution is to get them 
fixed in BIOS.

Regards,
Weidong


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