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Re: [XEN PATCH v2 08/15] x86/vpmu: guard vmx/svm calls with cpu_has_{vmx,svm}
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 May 2024 09:25:47 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>, Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
- Delivery-date: Thu, 16 May 2024 07:25:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.05.2024 02:44, Stefano Stabellini wrote:
> On Wed, 15 May 2024, Sergiy Kibrik wrote:
>> If VMX/SVM disabled in the build, we may still want to have vPMU drivers for
>> PV guests. Yet some calls to vmx/svm-related routines needs to be guarded
>> then.
>>
>> Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
>
> Question to the x86 maintainers: are we sure we want to support the case
> where VMX/SVM is disabled in the build but still we want to run PV
> guests with vPMU?
>
> If the question is not, could we simplify this simply by making vpmu_amd
> dependent on CONFIG_SVM and vpmu_intel dependent on CONFIG_VMX?
>
> I realize that it is possible and technically correct to disable
> CONFIG_SVM (or VMX) to run on AMD hardware (or Intel) with plain PV
> guests only. But do we want to support it? I wonder if we could make
> things easier by avoiding to support this configuration until somebody
> asks for it.
I think we want to allow for such a configuration; whether that's deemed
a supported one is an orthogonal question. Much like you can set PV=n and
HVM=n at the same time, yielding a largely useless hypervisor (where
perhaps even the question of whether it's support may raise eyebrows).
Jan
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