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Re: [PATCH 10/22] x86/mapcache: initialise the mapcache for the idle domain
- To: Elias El Yandouzi <eliasely@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 11 Jan 2024 08:53:13 +0100
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- Cc: Hongyan Xia <hongyxia@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Wei Wang <wawei@xxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Julien Grall <julien@xxxxxxx>
- Delivery-date: Thu, 11 Jan 2024 07:53:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10.01.2024 17:24, Elias El Yandouzi wrote:
> On 22/12/2022 13:06, Jan Beulich wrote:
>> On 16.12.2022 12:48, Julien Grall wrote:
>>> --- a/xen/arch/x86/mm.c
>>> +++ b/xen/arch/x86/mm.c
>>> @@ -5963,6 +5963,9 @@ int create_perdomain_mapping(struct domain *d,
>>> unsigned long va,
>>> l3tab = __map_domain_page(pg);
>>> clear_page(l3tab);
>>> d->arch.perdomain_l3_pg = pg;
>>> + if ( is_idle_domain(d) )
>>> + idle_pg_table[l4_table_offset(PERDOMAIN_VIRT_START)] =
>>> + l4e_from_page(pg, __PAGE_HYPERVISOR_RW);
>>
>> Hmm, having an idle domain check here isn't very nice. I agree putting
>> it in arch_domain_create()'s respective conditional isn't very neat
>> either, but personally I'd consider this at least a little less bad.
>> And the layering violation aspect isn't much worse than that of setting
>> d->arch.ctxt_switch there as well.
>
> Why do you think it would be less bad to move it in
> arch_domain_create()? To me, it would make things worse as it would
> spread the mapping stuff across different functions.
Not sure what to add to what I said: create_perdomain_mapping() gaining
such a check is a layering violation to me. arch_domain_create() otoh
special cases the idle domain already.
Jan
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