Re: [PATCH v7 10/14] VT-d: free all-empty page tables

["Durrant, Paul" <xadimgnik@xxxxxxxxx>]

On 05/07/2022 13:48, Jan Beulich wrote:
> When a page table ends up with no present entries left, it can be
> replaced by a non-present entry at the next higher level. The page table
> itself can then be scheduled for freeing.
>
> Note that while its output isn't used there yet,
> pt_update_contig_markers() right away needs to be called in all places
> where entries get updated, not just the one where entries get cleared.
>
> Note further that while pt_update_contig_markers() updates perhaps
> several PTEs within the table, since these are changes to "avail" bits
> only I do not think that cache flushing would be needed afterwards. Such
> cache flushing (of entire pages, unless adding yet more logic to me more
> selective) would be quite noticable performance-wise (very prominent
> during Dom0 boot).
>
> Also note that cache sync-ing is likely more strict than necessary. This
> is both to be on the safe side as well as to maintain the pattern of all
> updates of (potentially) live tables being accompanied by a flush (if so
> needed).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Paul Durrant <paul@xxxxxxx>