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Re: [XEN PATCH v4 02/14] x86/altp2m: add static inline stub for altp2m_vcpu_idx()
- To: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 9 Jul 2024 09:09:45 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 09 Jul 2024 07:10:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09.07.2024 07:48, Sergiy Kibrik wrote:
> The stub just returns 0 due to implementation of p2m_get_mem_access() for
> x86 & ARM expects it to be 0 when altp2m not active or not implemented.
>
> The separate stub is favoured over dynamic check for alt2pm availability
> inside regular altp2m_vcpu_idx() because this way we retain the possibility
> to later put the whole struct altp2mvcpu under CONFIG_ALTP2M.
>
> The purpose of the change is later to be able to disable altp2m support and
> exclude its code from the build completely, when not supported by target
> platform (as of now it's implemented for Intel EPT only).
>
> Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
Yet what doesn't become clear is why 0 is a valid value to return. On the
surface 0 is a valid index when altp2m is enabled. In which case it
couldn't be used (without clarification) when altp2m is disabled.
Jan
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