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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 15 Mar 2021, Jan Beulich wrote:
> On 13.03.2021 00:16, 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>
> > CC: jbeulich@xxxxxxxx
> > CC: andrew.cooper3@xxxxxxxxxx
> > CC: julien@xxxxxxx
> 
> Any particular reason my previously given R-b isn't here?

Hi Jan,

I reworded part of the comment in the public header, and I decided to
err on the side of caution and not add your R-b given this change
compared to the previous version.