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Re: [PATCH 2/3] xen/arm, tools: Add a new HVM_PARAM_MAGIC_BASE_PFN key in HVMOP
- To: Henry Wang <xin.wang2@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 26 Apr 2024 08:50:33 +0200
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Alec Kwapis <alec.kwapis@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 26 Apr 2024 06:50:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.04.2024 08:30, Henry Wang wrote:
> On 4/26/2024 2:21 PM, Jan Beulich wrote:
>> On 26.04.2024 05:14, Henry Wang wrote:
>>> --- a/xen/include/public/hvm/params.h
>>> +++ b/xen/include/public/hvm/params.h
>>> @@ -76,6 +76,7 @@
>>> */
>>> #define HVM_PARAM_STORE_PFN 1
>>> #define HVM_PARAM_STORE_EVTCHN 2
>>> +#define HVM_PARAM_MAGIC_BASE_PFN 3
>>>
>>> #define HVM_PARAM_IOREQ_PFN 5
>> Considering all adjacent values are used, it is overwhelmingly likely that
>> 3 was once used, too. Such re-use needs to be done carefully. Since you
>> need this for Arm only, that's likely okay, but doesn't go without (a)
>> saying and (b) considering the possible future case of dom0less becoming
>> arch-agnostic, or hyperlaunch wanting to extend the scope. Plus (c) imo
>> this also needs at least a comment, maybe even an #ifdef, seeing how x86-
>> focused most of the rest of this header is.
>
> Thanks for the feedback. These make sense. I think probably
> dom0less/hyperlaunch will have similar use cases so the number 3 can be
> reused at that time. Therefore, in v2, I will add more description in
> commit message, a comment on top of this macro and protect it with
> #ifdef. Hope this will address your concern. Thanks.
FTAOD: If you foresee re-use by hyperlaunch, re-using a previously used
number may need re-considering. Which isn't to say that number re-use is
excluded here, but it would need at least figuring out (and then stating)
what exactly the number was used for and until when.
Jan
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