Re: [PATCH 11/22] x86: add a boot option to enable and disable the direct map

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.01.2024 11:47, Elias El Yandouzi wrote:
> On 22/12/2022 13:24, Jan Beulich wrote:
>> That said, I think this change comes too early in the series, or there is
>> something missing. 
> 
> At first, I had the same feeling but looking at the rest of the series, 
> I can see that the option is needed in follow-up patches.
> 
>> As said in reply to patch 10, while there the mapcache
>> is being initialized for the idle domain, I don't think it can be used
>> just yet. Read through mapcache_current_vcpu() to understand why I think
>> that way, paying particular attention to the ASSERT() near the end.
> 
> Would be able to elaborate a bit more why you think that? I haven't been 
> able to get your point.

Why exactly I referred to the ASSERT() there I can't reconstruct. The
function as a whole looks problematic though when suddenly the idle
domain also gains a mapcache. I'm sorry, too much context was lost
from over a year ago; all of this will need looking at from scratch
again whenever a new version was posted.

>> In preparation of this patch here I think the mfn_to_virt() uses have to all
>> disappear from map_domain_page(). Perhaps yet more strongly all
>> ..._to_virt() (except fix_to_virt() and friends) and __va() have to
>> disappear up front from x86 and any code path which can be taken on x86
>> (which may simply mean purging all respective x86 #define-s, without
>> breaking the build in any way).
> 
> I agree with you on that one. I think it is what we're aiming for in the 
> long term. However, as mentioned by Julien in the cover letter, the 
> series's name is a misnomer and I am afraid we won't be able to remove 
> all of them with this series. These helpers would still be used for 
> xenheap pages or when the direct map is enabled.

Leaving a hazard of certain uses not having been converted, or even
overlooked in patches going in at around the same time as this series?
I view this as pretty "adventurous".

Jan