On Tue, 2017-11-14 at 20:40 +0100, David Hildenbrand wrote: > On 14.11.2017 19:07, Rik van Riel wrote: > > 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 :) > > > I think we should check all get/put_fpu callers if they need > preempt_disable(). > > E.g. em_fxrstor() needs disabled preemption as we temporarily > save + restore some host register (via fxsave + fxrstor) under some > circumstances that are not saved/restored when switching to/back from > another process. We should double check. > > @Paolo what about complete_userspace_io? It can end up calling > emulate_instruction(). So maybe we have to move load/put fpu further > out > or add special handling. It looks like all complete_userspace_io causes is for the vcpu_run loop to exit, and return to userspace from the KVM_RUN ioctl code. In other words, the userspace qemu FPU context should be restored before we return to userspace, even with my patch (v2 on the way). -- All rights reversed
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