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Re: [RFC PATCH 0/3] Add migration support for VFIO PCI devices in SMMUv3

From: Kunkun Jiang
Subject: Re: [RFC PATCH 0/3] Add migration support for VFIO PCI devices in SMMUv3 nested stage mode
Date: Mon, 12 Apr 2021 21:46:51 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1

Hi Eric,

On 2021/4/12 16:40, Auger Eric wrote:
Hi Kunkun,

On 2/19/21 10:42 AM, Kunkun Jiang wrote:
Hi all,

Since the SMMUv3's nested translation stages[1] has been introduced by Eric, we
need to pay attention to the migration of VFIO PCI devices in SMMUv3 nested 
mode. At present, it is not yet supported in QEMU. There are two problems in the
existing framework.

First, the current way to get dirty pages is not applicable to nested stage 
Because of the "Caching Mode", VTD can map the RAM through the host single stage
(giova->hpa). "vfio_listener_log_sync" gets dirty pages by transferring "giova"
to the kernel for the RAM block section of mapped MMIO region. In nested stage
mode, we setup the stage 2 (gpa->hpa) and the stage 1(giova->gpa) separately. So
it is inapplicable to get dirty pages by the current way in nested stage mode.

Second, it also need to pass stage 1 configurations to the destination host 
the migration. In Eric's patch, it passes the stage 1 configuration to the host 
each STE update for the devices set the PASID PciOps. The configuration will be
applied at physical level. But the data of physical level will not be sent to 
destination host. So we have to pass stage 1 configurations to the destination
host after the migration.

This Patch set includes patches as below:
Patch 1-2:
- Refactor the vfio_listener_log_sync and added a new function to get dirty 
in nested stage mode.

Patch 3:
- Added the post_load function to vmstate_smmuv3 for passing stage 1 
to the destination host after the migration.

@Eric, Could you please add this Patch set to your future version of
"vSMMUv3/pSMMUv3 2 stage VFIO integration", if you think this Patch set makes 
sense? :)
First of all, thank you for working on this. As you may have noticed I
sent a new RFC version yesterday (without including this). When time
allows, you may have a look at the comments I posted on your series. I
don't think I can test it at the moment so I may prefer to keep it
separate. Also be aware that the QEMU integration of nested has not
received much comments yet and is likely to evolve. The priority is to
get some R-b's on the kernel pieces, especially the SMMU part. With this
dependency resolved, things can't move forward I am afraid.


Yes, I saw your latest version and comments. Thanks again for your review.

I will try my best to test your patches and come up with some useful ideas.
In the future, this series will be updated with your series of nested.
If conditions permit, I hope you can test it and give me some comments.

Best regards,
Kunkun Jiang
Best Regards
Kunkun Jiang

[1] [RFC,v7,00/26] vSMMUv3/pSMMUv3 2 stage VFIO integration

Kunkun Jiang (3):
   vfio: Introduce helpers to mark dirty pages of a RAM section
   vfio: Add vfio_prereg_listener_log_sync in nested stage
   hw/arm/smmuv3: Post-load stage 1 configurations to the host

  hw/arm/smmuv3.c     | 60 +++++++++++++++++++++++++++++++++++++++++++++
  hw/arm/trace-events |  1 +
  hw/vfio/common.c    | 47 +++++++++++++++++++++++++++++------
  3 files changed, 100 insertions(+), 8 deletions(-)


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