On Wed, Oct 25, 2023 at 05:52:58PM +0900, Hyesoo Yu wrote:

If we only avoid using ALLOC_CMA for __GFP_TAGGED, would we still be able to use
the next iteration even if the hardware does not support "tag of tag" ? 

It depends on how the next iteration looks like. The plan was not to
support this so that we avoid another complication where a non-tagged
page is mprotect'ed to become tagged and it would need to be migrated
out of the CMA range. Not sure how much code it would save.

I am not sure every vendor will support tag of tag, since there is no information
related to that feature, like in the Google spec document.

If you are aware of any vendors not supporting this, please direct them
to the Arm support team, it would be very useful information for us.

Thanks.

-- 
Catalin