Re: [PATCH 4/4] Hack around IOMMU changes

[Jan Kiszka <jan.kiszka@web.de>]

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Zachary Amsden wrote:
> On 05/25/2010 09:40 PM, Jan Kiszka wrote:
>> Zachary Amsden wrote:
>>   
>>> On 05/25/2010 05:36 PM, Zachary Amsden wrote:
>>>     
>>>> Not for the faint of heart, this patch subverts the code by
>>>> reassigning a local variable from a macro.
>>>>        
>>> This time, with patch.
>>>
>>>
>>>  From 97b9230f699aba1c5f47972032b2d4d935a83054 Mon Sep 17 00:00:00 2001
>>> From: Zachary Amsden<zamsden@redhat.com>
>>> Date: Tue, 25 May 2010 17:17:32 -1000
>>> Subject: [PATCH 4/5] IOMMU API changed
>>>
>>> Ugly, dirty, disease ridden fix for IOMMU changes; the module
>>> is now trying to use larger IOMMU intervals; deny it this, and
>>> stick to page size.  This requires forcibly setting page_size
>>> variable through knowledge of the code.  Yuck.  If you have a
>>> better solution, implement it.
>>>
>>> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
>>> ---
>>>   external-module-compat-comm.h |   12 ++++++++++++
>>>   1 files changed, 12 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/external-module-compat-comm.h
>>> b/external-module-compat-comm.h
>>> index c5284e5..708019e 100644
>>> --- a/external-module-compat-comm.h
>>> +++ b/external-module-compat-comm.h
>>> @@ -1128,3 +1128,15 @@ perf_unregister_guest_info_callbacks(struct
>>> perf_guest_info_callbacks *cbs)
>>>   #if LINUX_VERSION_CODE<  KERNEL_VERSION(2,6,32)
>>>   #define lockdep_is_held(m)        (1)
>>>   #endif
>>> +
>>> +#if LINUX_VERSION_CODE<  KERNEL_VERSION(2,6,34)
>>> +/* This is a dirty, nasty trick */
>>> +#define iommu_map(domain, iova, paddr, gfp_order, prot) \
>>> +({ \
>>> +    int _r = iommu_map_range(domain, iova, paddr, PAGE_SIZE, prot); \
>>>      
>> This should be (PAGE_SIZE<<  gfp_order) according to my current
>> understanding.
>>    
> 
> It should, but can't be.
>>   
>>> +    page_size = PAGE_SIZE; \
>>>      
>> And what is this for?
>>    
> 
> iommu_unmap is now passed an unreasonable value for order: PAGE_SIZE. 

Indeed. This is an upstream bug and has to be fixed instead of worked
around. I'll send a patch.

Jan

PS: If there were already a KVM release with this included, the more
appropriate way for kvm-kmod to deal with it would be patching the
particular code line during sync.


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