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

[Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>]

On 16.12.25 17:00, Harry Ramsey wrote:

Hello Harry

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> 
> 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>

Thank you very much for testing on the Arm32 platform and confirming 
that the proposed size is sufficient!


> 
> Thanks,
> Harry Ramsey