On Tue, 2017-11-14 at 17:57 +0100, David Hildenbrand wrote: > > > diff --git a/arch/x86/include/asm/kvm_host.h > > b/arch/x86/include/asm/kvm_host.h > > index c73e493adf07..92e66685249e 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > We should also get rid of guest_fpu_loaded now, right? Indeed, we no longer need that member. I'll get rid of it. > emulator_get_fpu() does a kvm_load_guest_fpu(). Doesn't that mean > that > this is now not needed anymore? (at least when emulator code is > called > from inside the loop?) Now that is a very good question! When called from inside the loop, it is indeed not needed. My question is, can the in-kernel emulator code ever be called from OUTSIDE the KVM_RUN ioctl loop? If so, we need to restore the user FPU context before returning from the emulator code. Given that the current emulator code does not do that, I suspect this is not the case. I also see no path from the kvm ioctl into the emulator code, other than via KVM_RUN. The FPU and XSAVE ioctls all work on the saved vcpu->arch.guest_fpu data, and never directly on the registers. Looks like we can completely get rid of .get_fpu and .put_fpu... Unless Paolo has any objection, I'll go do that :) > Also, what about preempt_diable() at that point, still needed? If the guest FPU context is the only FPU context loaded for the task at that point in time, we should not need to run with preemption disabled. After all, if we were to get preempted, the context switch code would automatically save and restore the guest FPU context for us. -- All rights reversed
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