On Fri, Mar 11, 2016 at 1:14 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > On Fri, Mar 11, 2016 at 12:47 PM, David Matlack <dmatlack@xxxxxxxxxx> wrote: > > From: Eric Northup <digitaleric@xxxxxxxxxx> > > > > Add a percpu boolean, tracking whether a KVM vCPU is running on the > > host CPU. KVM will set and clear it as it loads/unloads guest XCR0. > > (Note that the rest of the guest FPU load/restore is safe, because > > kvm_load_guest_fpu and kvm_put_guest_fpu call __kernel_fpu_begin() > > and __kernel_fpu_end(), respectively.) irq_fpu_usable() will then > > also check for this percpu boolean. > > Is this better than just always keeping the host's XCR0 loaded outside > if the KVM interrupts-disabled region? Probably not. AFAICT KVM does not rely on it being loaded outside that region. xsetbv isn't insanely expensive, is it? Maybe to minimize the time spent with interrupts disabled it was put outside. I do like that your solution would be contained to KVM. > > --Andy -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
