On Wed, Aug 16, 2017 at 09:14:41AM -0700, Andy Lutomirski wrote: > On Wed, Aug 16, 2017 at 5:57 AM, Matt Fleming <m...@codeblueprint.co.uk> > wrote: > > On Wed, 16 Aug, at 12:03:22PM, Mark Rutland wrote: > >> > >> I'd expect we'd abort at a higher level, not taking any sample. i.e. > >> we'd have the core overflow handler check in_funny_mm(), and if so, skip > >> the sample, as with the skid case. > > > > FYI, this is my preferred solution for x86 too. > > One option for the "funny mm" flag would be literally the condition > current->mm != current->active_mm. I *think* this gets all the cases > right as long as efi_switch_mm is careful with its ordering and that > the arch switch_mm() code can handle the resulting ordering. (x86's > can now, I think, or at least will be able to in 4.14 -- not sure > about other arches).
For arm64 we'd have to rework things a bit to get the ordering right (especially when we flip to/from the idmap), but otherwise this sounds sane to me. > That being said, there's a totally different solution: run EFI > callbacks in a kernel thread. This has other benefits: we could run > those callbacks in user mode some day, and doing *that* in a user > thread seems like a mistake. I think that wouldn't work for CPU-bound perf events (which are not ctx-switched with the task). It might be desireable to do that anyway, though. Thanks, Mark.
