Re: QEMU virt (arm64) does not honor reserved-memory set in device tree

[Mohd Yusuf Abdul Hamid]

Hi Gavin,

Thanks for the reply. I am new to Linux dev in general and not familiar with the ACPI table, but I will research in the area and give it a try.

Sorry for the late response.

-Yusuf

On Fri, Jun 9, 2023, 8:36 PM Gavin Shan <gshan@redhat.com> wrote:

Hi Mohd,

On 6/10/23 10:01 AM, Mohd Yusuf Abdul Hamid wrote:
> I am trying to reserve a portion of the system memory in QEMU (arm64 virt), v7.2.1 - but the kernel never honors the reserved memory area and keeps using the area.
>
> Say, I dumped out DTB and added:
>
> reserved-memory {
>    #address-cells = <0x02>;
>    #size-cells = <0x02>;
>
>    rsvdram@50000000 {
>    no-map;
>    reg = <0x00 0x50000000 0x00 0x20000000>;
>    };
> };
>
> When booted, /proc/iomem still shows the kernel is using the entire space - eg 2GB.
>
> Is this a supported feature or I would need to modify the virt.c and define scratch area for some device driver scratch area.
>

It relies on the guest kernel to handle the device-tree and the device-tree node
for the reserved map. I doubt if you had ACPI over device-tree in the guest kernel's
configuration. In this case, the reserved memory regions need to be specified in
ACPI tables instead of device-tree.

Thanks,
Gavin