Re: [Xen-devel] Commit dd6d87 breaks serial console

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Roger Pau Monné wrote on 2014-07-15:
> On 14/07/14 18:25, Andrew Cooper wrote:
>> On 14/07/14 17:07, Roger Pau Monné wrote:
>>> Hello,
>>> 
>>> The following commit:
>>> 
>>> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
>>> Author: Jan Beulich <jbeulich@xxxxxxxx>
>>> Date:   Fri Jun 20 10:26:37 2014 +0200
>>> 
>>>     VT-d: drop redundant calls to invalidate_sync()
>>>     
>>>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>>>     invokes invalidate_sync(). Removing the superfluous instances at once
>>>     allows the function to become static.
>>>     
>>>     Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>     Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>     Acked-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>>> Breaks serial console on my box, this is all the output I get with
>>> this commit applied:
>> 
>> Are you sure you have bisected this correctly?
>> 
>> Unless there is some hardware side-effect of issuing two qinvalidate
>> wait descriptors back-to-back, the change still looks to be good.
>> Alternately, are we missing a hardware erratum for your system?
> 
> Just for the record, setting iommu=no-intremap solves the problem, so
> I'm quite sure I've bisected it right. This is on a Xeon W3550, I can
> provide whatever other hardware information is needed.

It is so strange. The patch is really simple. Does Xen still alive when serial 
console breaks? Also, can you try to add invalidate_sync one by one to figure 
which one caused the problem?

> 
> Roger.


Best regards,
Yang


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