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. --Andy -- 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
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