Re: [Qemu-arm] [RFC v2 0/6] hw/arm: Add support for non-contiguous iova regions

[Auger Eric <eric.auger@redhat.com>]

Hi Shameer,

On 05/16/2018 05:20 PM, Shameer Kolothum wrote:
> When the kernel reports valid iova ranges as non-contiguous,
> memory should be allocated to Guest in such a way that
> reserved regions(holes) are not visible by Guest.
> 
> This series retrieves the valid iova ranges based on the new
> proposed VFIO interface for kernel [1]. It then populates the
> first 1GB ram as a non-pluggable dimm and rest as a pc-dimm if
> the valid iova ranges are non-contiguous.

Some general comments:

- what are your plans with respect to VFIO device hot-plug handling?
IIUC, at the moment, any collision between reserved regions induces by
hot-plugged devices are not detected/handled. I understand mem hotplug
is not supported on aarch64. Would you simply reject the vfio device
hotplug.

- IIUC any reserved window colliding with [4000000, 1GB] cold-plug RAM
segment is show-stopper. How was this 1GB size chosen exactly?

- Currently you create a single PC-DIMM node whereas several ones may be
possible & necessary? Do you plan to support multiple PC-DIMMS node?

- I have started looking at RAM extension on machvirt. I think adding
support of PC-DIMMS through the qemu cmd line is something that we need
to work on, in paralell.

Thanks

Eric
> 
> Patch #3 of this series is loosely based on an earlier attempt
> by Kwangwoo Lee to add hotplug/pc-dimm support to arm64[2]
> 
> RFC v1[3] --> RFCv2
>  -Based on new VFIO kernel interface
>  -Part of Mem modelled as pc-dimm 
>  -Rebased to qemu 2.12.0
> 
> [1] https://lkml.org/lkml/2018/4/18/293
> [2] https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg04600.html
> [3] https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg02412.html
> 
> Shameer Kolothum (6):
>   hw/vfio: Retrieve valid iova ranges from kernel
>   hw/arm/virt: Enable dynamic generation of guest RAM memory regions
>   hw/arm/virt: Add pc-dimm mem hotplug framework
>   hw/arm: Changes required to accommodate non-contiguous DT mem nodes
>   hw/arm: ACPI SRAT changes to accommodate non-contiguous mem
>   hw/arm: Populate non-contiguous memory regions
> 
>  default-configs/aarch64-softmmu.mak |   1 +
>  hw/arm/boot.c                       |  91 ++++++---
>  hw/arm/virt-acpi-build.c            |  24 ++-
>  hw/arm/virt.c                       | 367 +++++++++++++++++++++++++++++++++++-
>  hw/vfio/common.c                    | 108 ++++++++++-
>  include/hw/arm/arm.h                |  12 ++
>  include/hw/arm/virt.h               |   3 +
>  include/hw/vfio/vfio-common.h       |   7 +
>  linux-headers/linux/vfio.h          |  23 +++
>  9 files changed, 589 insertions(+), 47 deletions(-)
>