Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0

From: David Matlack
Date: Wed Mar 16 2016 - 13:11:59 EST

On Tue, Mar 15, 2016 at 8:48 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> Why is it safe to rely on interrupted_kernel_fpu_idle? That function
> is for interrupts, but is there any reason that KVM can't be preempted
> (or explicitly schedule) with XCR0 having some funny value?

KVM restores the host's xcr0 in the sched-out preempt notifier and
prior to returning to userspace.