On 06/05/2014 09:18 AM, Borislav Petkov wrote: > On Thu, Jun 05, 2014 at 09:14:51AM -0700, Andy Lutomirski wrote: >> Is this NMI pstore thing done from any context that's supposed to be >> recoverable? It's always safe to use the FPU and then panic :) > > Right :) > >> Anyway, if we're just talking about EFI, there's an easier solution: >> just preallocate a per-cpu FPU context for EFI and make the whole mess >> be local to the EFI code. For crypto, that's not so good. > > This is probably something for Matt to decide but it sounds doable. If > I'd have to guess, sooner or later we will need to do proper FPU context > handling for EFI as I don't see anything stopping it from using FPU > insns. At least we won't. :-) > The bottom line is that we can't call EFI from a context where we can't use the FPU. Or specifically, we can't then resume execution. If all we're doing is stashing away some data before dying, well, then, by all means - but we need to make sure that is what actually happens. As far adding additional xstate save areas, the current size of the xstate is about ~2.5K for AVX-512 enabled processors, and we need one per thread. If we make that two copies, then kernel_fpu_begin()..._end() would no longer have to disable preemption, but it wouldn't resolve the conflict about using the FPU from IRQ context when inside kernel_fpu_begin().._end(). To support the FPU in IRQ context we end up having to create a percpu FPU state stack, and it becomes then a matter of how deep that stack would have to be. -hpa -- 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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