[Qemu-devel] [Bug 1762707] [NEW] VFIO device gets DMA failures when virtio-balloon leak from highmem to lowmem

[Pixel, Ding]

Public bug reported:

Is there any known conflict between VFIO passthrough device and virtio-
balloon?

The VM has:
1. 4GB system memory
2. one VFIO passthrough device which supports high address memory DMA and uses 
GFP_HIGHUSER pages.
3. Memory balloon device with 4GB target.

When setting the memory balloon target to 1GB and 4GB in loop during
runtime (I used the command "virsh qemu-monitor-command debian --hmp
--cmd balloon 1024"), the VFIO device DMA randomly gets failure.

More clues:
1. configure 2GB system memory (no highmem) VM, no issue with similar operations
2. setting the memory balloon to higher like 8GB, no issue with similar 
operations

I'm also trying to narrow down this issue. It's appreciated for that you
guys may share some thoughts.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1762707

Title:
  VFIO device gets DMA failures when virtio-balloon leak from highmem to
  lowmem

Status in QEMU:
  New

Bug description:
  Is there any known conflict between VFIO passthrough device and
  virtio-balloon?

  The VM has:
  1. 4GB system memory
  2. one VFIO passthrough device which supports high address memory DMA and 
uses GFP_HIGHUSER pages.
  3. Memory balloon device with 4GB target.

  When setting the memory balloon target to 1GB and 4GB in loop during
  runtime (I used the command "virsh qemu-monitor-command debian --hmp
  --cmd balloon 1024"), the VFIO device DMA randomly gets failure.

  More clues:
  1. configure 2GB system memory (no highmem) VM, no issue with similar 
operations
  2. setting the memory balloon to higher like 8GB, no issue with similar 
operations

  I'm also trying to narrow down this issue. It's appreciated for that
  you guys may share some thoughts.

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