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

[Gavin Shan]

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