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Re: [PATCH v5] x86: make Viridian support optional
- To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 17 Oct 2025 08:01:13 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- Delivery-date: Fri, 17 Oct 2025 06:01:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.10.2025 00:38, Marek Marczykowski-Górecki wrote:
> On Fri, Oct 17, 2025 at 12:40:33AM +0300, Grygorii Strashko wrote:
>> Another point, assume change like this is to be done for HVM_PARAM_VIRIDIAN
>> - there are another HVM_PARAM_x which depend on build-time disabled
>> features, like:
>> HVM_PARAM_VM86_TSS_SIZED
>> HVM_PARAM_PAGING_RING_PFN,
>> HVM_PARAM_MONITOR_RING_PFN,
>> HVM_PARAM_SHARING_RING_PFN,
>> HVM_PARAM_IDENT_PT
>> ...
>>
>> if corresponding features are build-time disabled, above HVM_PARAM_x
>> become R/W with functionality NOP now.
>
> Are you sure? For me it looks like setting build-time disabled feature
> returns -ENOSYS. Or do you mean some other interface than
> xc_hvm_param_set().
Where do you see that ENOSYS coming from? In fact, for example, I don't see any
of the *_RING_PFN even mentioned at all in hvm.c's parameter handling. Are you
perhaps thinking of only the HVM=n case, whereas I expect Grygorii talks about
the more fine-grained controls?
That said, whether to uniformly fail requests for params solely related to
build-time disabled features isn't quite clear. Arguably for e.g. paging and
sharing, setting the ring PFN can as well be silently ignored (no events ever
appearing), while failure would then be reported from other compiled-out logic.
Jan
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