Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends

2020-09-24 Thread peterz
On Wed, Sep 23, 2020 at 11:52:51AM -0400, Steven Rostedt wrote: > On Wed, 23 Sep 2020 10:40:32 +0200 > pet...@infradead.org wrote: > > > However, with migrate_disable() we can have each task preempted in a > > migrate_disable() region, worse we can stack them all on the _same_ CPU > > (super

Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends

2020-09-23 Thread peterz
On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote: > Alternatively this could of course be solved with per CPU page tables > which will come around some day anyway I fear. Previously (with PTI) we looked at making the entire kernel map per-CPU, and that takes a 2K copy on

Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends

2020-09-23 Thread peterz
On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote: > On Mon, Sep 21 2020 at 09:24, Linus Torvalds wrote: > > On Mon, Sep 21, 2020 at 12:39 AM Thomas Gleixner wrote: > >> > >> If a task is migrated to a different CPU then the mapping address will > >> change which will explode in