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Re: [PATCH] xen/arm: p2m: Populate pages for GICv2 mapping in arch_domain_create()
- To: Henry Wang <Henry.Wang@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 13 Oct 2022 13:36:28 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>
- Delivery-date: Thu, 13 Oct 2022 11:36:35 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.10.2022 13:05, Henry Wang wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Subject: Re: [PATCH] xen/arm: p2m: Populate pages for GICv2 mapping in
>> arch_domain_create()
>>
>> On 13.10.2022 12:58, Julien Grall wrote:
>>> On 13/10/2022 10:21, Henry Wang wrote:
>>>>> -----Original Message-----
>>>>> From: Julien Grall <julien@xxxxxxx>
>>>>> Subject: Re: [PATCH] xen/arm: p2m: Populate pages for GICv2 mapping
>> in
>>>>> arch_domain_create()
>>>>>
>>>>> On 13/10/2022 09:38, Henry Wang wrote:
>>>>>> Hardware using GICv2 needs to create a P2M mapping of 8KB GICv2
>> area
>>>>>> when the domain is created. Considering the worst case of page tables
>>>>>
>>>>> Can you describe in the commit message what is the worst case scenario?
>>>>
>>>> The two pages will be consecutive but not necessarily in the same L3 page
>>>> table so the worst case is 4 + 2, is that correct?
>>>
>>> So I agree that the worse case is 6. But I don't understand what you
>>> mean by '4 + 2' here.
>>
>> Assuming you have 4 (N) page table levels, isn't it 7 (1 + 2 * (N - 1))?
>> Or is the root table not taken from the p2m pool?
>
> Correct, on arm the root is not taken from the pool.
Isn't that a (perhaps just minor) mistake?
Jan
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