On Tue, Jun 23, 2020 at 04:39:26PM +0100, Andrew Cooper wrote: > On 23/06/2020 16:23, Peter Zijlstra wrote: > > On Tue, Jun 23, 2020 at 04:59:14PM +0200, Joerg Roedel wrote: > >> Yes, this is a start, it doesn't cover the case where the NMI stack is > >> in-between, so I think you need to walk down regs->sp too. > > That shouldn't be possible with the current code, I think. > > NMI; #MC; Anything which IRET but isn't fatal - #DB, or #BP from > patching, #GP from *_safe(), etc; NMI > > Sure its a corner case, but did you hear that IST is evil? Isn't current #MC unconditionally fatal from kernel? But yes, I was sorta aware people want that changed. And yes, NMI can recurse, mostly on #BP and #PF. Like I wrote, its broken vs #MC. But Joerg was talking about IST recursion with NMI in the middle, something like: #DB, NMI, #DB, and not already being fatal. This one in particular is ruled out by #DB itself clearing DR7 (but NMI would also do that). > P.S. did you also hear that with Rowhammer, userspace has a nonzero > quantity of control over generating #MC, depending on how ECC is > configured on the platform. Yes, excellent stuff.
