Re: [PATCH V2] xen/dom0less: Calculate guest DTB size based on MAX_VIRT_CPUS

[Harry Ramsey <harry.ramsey@xxxxxxx>]

On 04/12/2025 13:37, Oleksandr Tyshchenko wrote:
> Thank you very much for offering to test this on Arm32 platforms.
>
> The primary goal of the test is to confirm that the new, calculated DTB
> buffer size of 3072 bytes is sufficient for a worst-case Arm32 dom0less
> guest. The expected result is that Xen boots successfully, and the
> regular dom0less guest is created without any panics.
>
> The ideal test configuration would be a dom0less guest with the
> following configuration:
> - The vCPU count set to the maximum for Arm32, which is 8, the vCPU
> nodes should ideally contain "clock-frequency" property.
> - Any other features that add nodes to the guest device tree enabled
> (e.g., hypervisor, reserved-memory, pl011 nodes are present, etc), to
> create the largest possible "base" FDT size.
>
> The test would involve applying the current patch, and the diff below:
>
> diff --git a/xen/common/device-tree/dom0less-build.c
> b/xen/common/device-tree/dom0less-build.c
> index 38a5830813..e95f42d1e1 100644
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -577,6 +577,9 @@ static int __init prepare_dtb_domU(struct domain *d,
> struct kernel_info *kinfo)
>        if ( ret < 0 )
>            goto err;
>
> +    printk("Final compacted FDT size is: %d bytes\n",
> fdt_totalsize(kinfo->fdt));
> +    printk("Predefined FDT size is: %d bytes\n", DOMU_DTB_SIZE);
> +
>        return 0;
>
>      err:
>
>
> Please let me know what you get. Thanks again.
I have tested this and can confirm it boots into Linux with an 8-core 
setup. Here are the values I got:
(XEN) Final compacted FDT size is: 1127 bytes
(XEN) Predefined FDT size is: 3072 bytes

Tested-by: Harry Ramsey <harry.ramsey@xxxxxxx>

Thanks,
Harry Ramsey