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Re: [PATCH V2] xen/dom0less: Calculate guest DTB size based on MAX_VIRT_CPUS
- To: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Thu, 4 Dec 2025 08:44:41 +0000
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- Cc: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
- Delivery-date: Thu, 04 Dec 2025 08:45:59 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH V2] xen/dom0less: Calculate guest DTB size based on MAX_VIRT_CPUS
Hi Oleksandr,
>
>>
>>> */
>>> -#define DOMU_DTB_SIZE 4096
>>> +#define DOMU_DTB_SIZE (2048 + (MAX_VIRT_CPUS * 128))
>>
>> On Arm32, MAX_VIRT_CPUS is 8. This means the new DOMU_DTB_SIZE is going
>> to be smaller than 4096. Why is it ok?
>
> You are correct to question the impact on Arm32, where MAX_VIRT_CPUS is
> smaller, leading to a calculated buffer size of 3072 bytes, which is
> less than the original 4096 bytes.
>
> Unfortunately, I have no possibility to test on Arm32. But, I do not see
> much difference between Arm64 and Arm32 in the context of DomU device
> tree generation by looking into the code.
Let me know what kind of test you need, we have some arm32 setup here (not HW,
virtual platforms).
Cheers,
Luca
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