On Wed, Jun 04, 2014 at 05:19:01PM -0700, Andy Lutomirski wrote: > On 06/04/2014 03:49 PM, Borislav Petkov wrote: > > On Wed, Jun 04, 2014 at 03:17:30PM -0700, H. Peter Anvin wrote: > >> I seem to have lost track of this... does this actually solve > >> anything, or does it just mean we'll explode hard? > > > > Not that hard - it'll warn once only. > > > > AFAIR, the discussion stalled but we were going in the direction of not > > calling into efi from pstore in irq context. > > The kernel_fpu_begin thing has annoyed me in the past. How bad would it > be to allocate some percpu space and just do a full save/restore when > kernel_fpu_begin happens in a context where it currently doesn't work? > > I don't know how large the state is these days, but there must be some > limit to how deeply interrupts and exceptions can nest. For each IST > entry, there is a hard limit to how deeply they can nest (once for all > but debug and four times for debug IIRC), plus one NMI (nested ones > don't touch FPU). The most non-IST entries we can have must be bounded, > too. > > Let's say there are at most 16 levels of nesting. 16 * state size * > cpus isn't that much. > > Of course, code in interrupts that nests kernel_fpu_begin itself could > have a problem. But this can be solved with a little bit of trickery in > the entry code or something. > > If we did this, then I think the x86 crypto code could get rid of all of > its ridiculous async code. How are you going to detect when to save/restore state? Do it unconditionally would probably be a no-no. Even with all that optimized XSAVE* fun. On demand would mean you allow FPU exceptions which probably gravitates towards a no-no too. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html