On Tue, Aug 15, 2017 at 11:35:41PM +0100, Mark Rutland wrote: > On Wed, Aug 16, 2017 at 09:14:41AM -0700, Andy Lutomirski wrote: > > On Wed, Aug 16, 2017 at 5:57 AM, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> 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. I'm still concerned that we're treating perf specially here -- are we absolutely sure that nobody else is going to attempt user accesses off the back of an interrupt? If not, then I'd much prefer a solution that catches anybody doing that with the EFI page table installed, rather than trying to play whack-a-mole like this. Will -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
