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Subject: Re: [PATCH Kernel v22 0/8] Add UAPIs to support migration for VFIO
 devices
To: Yan Zhao <yan.y.zhao@intel.com>, Alex Williamson
 <alex.williamson@redhat.com>
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From: Kirti Wankhede <kwankhede@nvidia.com>
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Date: Thu, 21 May 2020 12:39:48 +0530
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On 5/21/2020 10:38 AM, Yan Zhao wrote:
> On Wed, May 20, 2020 at 10:46:12AM -0600, Alex Williamson wrote:
>> On Wed, 20 May 2020 19:10:07 +0530
>> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>>
>>> On 5/20/2020 8:25 AM, Yan Zhao wrote:
>>>> On Tue, May 19, 2020 at 10:58:04AM -0600, Alex Williamson wrote:
>>>>> Hi folks,
>>>>>
>>>>> My impression is that we're getting pretty close to a workable
>>>>> implementation here with v22 plus respins of patches 5, 6, and 8.  We
>>>>> also have a matching QEMU series and a proposal for a new i40e
>>>>> consumer, as well as I assume GVT-g updates happening internally at
>>>>> Intel.  I expect all of the latter needs further review and discussion,
>>>>> but we should be at the point where we can validate these proposed
>>>>> kernel interfaces.  Therefore I'd like to make a call for reviews so
>>>>> that we can get this wrapped up for the v5.8 merge window.  I know
>>>>> Connie has some outstanding documentation comments and I'd like to make
>>>>> sure everyone has an opportunity to check that their comments have been
>>>>> addressed and we don't discover any new blocking issues.  Please send
>>>>> your Acked-by/Reviewed-by/Tested-by tags if you're satisfied with this
>>>>> interface and implementation.  Thanks!
>>>>>   
>>>> hi Alex and Kirti,
>>>> after porting to qemu v22 and kernel v22, it is found out that
>>>> it can not even pass basic live migration test with error like
>>>>
>>>> "Failed to get dirty bitmap for iova: 0xca000 size: 0x3000 err: 22"
>>>>    
>>>
>>> Thanks for testing Yan.
>>> I think last moment change in below cause this failure
>>>
>>> https://lore.kernel.org/kvm/1589871178-8282-1-git-send-email-kwankhede@nvidia.com/
>>>
>>>   > 	if (dma->iova > iova + size)
>>>   > 		break;
>>>
>>> Surprisingly with my basic testing with 2G sys mem QEMU didn't raise
>>> abort on g_free, but I do hit this with large sys mem.
>>> With above change, that function iterated through next vfio_dma as well.
>>> Check should be as below:
>>>
>>> -               if (dma->iova > iova + size)
>>> +               if (dma->iova > iova + size -1)
>>
>>
>> Or just:
>>
>> 	if (dma->iova >= iova + size)
>>
>> Thanks,
>> Alex
>>
>>
>>>                           break;
>>>
>>> Another fix is in QEMU.
>>> https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg04751.html
>>>
>>>   > > +        range->bitmap.size = ROUND_UP(pages, 64) / 8;
>>>   >
>>>   > ROUND_UP(npages/8, sizeof(u64))?
>>>   >
>>>
>>> If npages < 8, npages/8 is 0 and ROUND_UP(0, 8) returns 0.
>>>
>>> Changing it as below
>>>
>>> -        range->bitmap.size = ROUND_UP(pages / 8, sizeof(uint64_t));
>>> +        range->bitmap.size = ROUND_UP(pages, sizeof(__u64) *
>>> BITS_PER_BYTE) /
>>> +                             BITS_PER_BYTE;
>>>
>>> I'm updating patches with these fixes and Cornelia's suggestion soon.
>>>
>>> Due to short of time I may not be able to address all the concerns
>>> raised on previous versions of QEMU, I'm trying make QEMU side code
>>> available for testing for others with latest kernel changes. Don't
>>> worry, I will revisit comments on QEMU patches. Right now first priority
>>> is to test kernel UAPI and prepare kernel patches for 5.8
>>>
>>
> hi Kirti
> by updating kernel/qemu to v23, still met below two types of errors.
> just basic migration test.
> (the guest VM size is 2G for all reported bugs).
> 
> "Failed to get dirty bitmap for iova: 0xfe011000 size: 0x3fb0 err: 22"
> 

size doesn't look correct here, below check should be failing.
  range.size & (iommu_pgsize - 1)

> or
> 
> "qemu-system-x86_64-lm: vfio_load_state: Error allocating buffer
> qemu-system-x86_64-lm: error while loading state section id 49(vfio)
> qemu-system-x86_64-lm: load of migration failed: Cannot allocate memory"
> 
> 

Above error is from:
         buf = g_try_malloc0(data_size);
         if (!buf) {
             error_report("%s: Error allocating buffer ", __func__);
             return -ENOMEM;
         }

Seems you are running out of memory?

Thanks,
Kirti