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Re: [RFC PATCH 4/9] hvm: Introduce "fixed memory layout" feature
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 20 Oct 2025 15:43:26 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 20 Oct 2025 13:43:35 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.10.2025 15:26, Teddy Astie wrote:
> Le 01/09/2025 à 17:50, Jan Beulich a écrit :
>> On 29.08.2025 15:32, Teddy Astie wrote:
>>> Le 28/08/2025 à 14:30, Jan Beulich a écrit :
>>>> On 21.08.2025 17:25, Teddy Astie wrote:
>>>>> --- a/xen/include/public/arch-x86/hvm/start_info.h
>>>>> +++ b/xen/include/public/arch-x86/hvm/start_info.h
>>>>> @@ -99,6 +99,13 @@
>>>>> #define XEN_HVM_MEMMAP_TYPE_DISABLED 6
>>>>> #define XEN_HVM_MEMMAP_TYPE_PMEM 7
>>>>>
>>>>> +/* Xen-specific types (OEM-specific range of the ACPI spec) */
>>>>> +#define XEN_HVM_MEMMAP_TYPE_SHARED_INFO 0xF0000001 /* Shared info page
>>>>> */
>>>>> +#define XEN_HVM_MEMMAP_TYPE_GRANT_TABLE 0xF0000002 /* Grant table
>>>>> pages */
>>>>> +#define XEN_HVM_MEMMAP_TYPE_GNTTAB_STATUS 0xF0000003 /* Grant table
>>>>> status page (v2) */
>>>>> +#define XEN_HVM_MEMMAP_TYPE_FOREIGN_REG 0xF0000004 /* Suitable region
>>>>> for grant mappings */
>>>>> + /* and foreign
>>>>> mappings */
>>>>
>>>> I question it being legitimate for us to introduce new E820 types.
>>>
>>> These E820 types are (at least in ACPI specification) in the OEM-defined
>>> range which seems appropriate for me to use for Xen-specific mappings.
>>
>> Just that we're not an OEM.
>
> How should such information be provided alternatively ?
>
> Currently, premapped pages (xenstore, PV console, ...) locations are
> provided through hvm parameters, but I don't think introducing new hvm
> parameters is very wise.
>
> One way of another, we would need to provide to the guest a xen-specific
> memory map for implementing this.
Yes, I don't think there's a way around something custom. (I am, btw, also
not overly happy about seeing "fixed memory layout" appear in the first
place.)
Jan
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