Re: [PATCH Kernel v22 0/8] Add UAPIs to support migration for VFIO devices

[Yan Zhao <yan.y.zhao@intel.com>]

On Thu, May 21, 2020 at 12:39:48PM +0530, Kirti Wankhede wrote:
> 
> 
> 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?
>
no. my host memory is about 60G.
just migrate with command "migrate -d xxx" without speed limit.
FYI.

Yan