Re: [PATCH v3] xen: introduce XENFEAT_direct_mapped and XENFEAT_not_direct_mapped

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 12/03/2021 23:16, Stefano Stabellini wrote:
> Introduce two feature flags to tell the domain whether it is
> direct-mapped or not. It allows the guest kernel to make informed
> decisions on things such as swiotlb-xen enablement.
>
> The introduction of both flags (XENFEAT_direct_mapped and
> XENFEAT_not_direct_mapped) allows the guest kernel to avoid any
> guesswork if one of the two is present, or fallback to the current
> checks if neither of them is present.
>
> XENFEAT_direct_mapped is always set for not auto-translated guests.
>
> For auto-translated guests, only Dom0 on ARM is direct-mapped. Also,
> see is_domain_direct_mapped() which refers to auto-translated guests:
> xen/include/asm-arm/domain.h:is_domain_direct_mapped
> xen/include/asm-x86/domain.h:is_domain_direct_mapped
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall