Re: [PATCH 2/5] KVM: x86: drop fpu_activate hook

[Avi Kivity]

On 08/18/2014 01:20 PM, Paolo Bonzini wrote:
> Il 18/08/2014 11:50, Wanpeng Li ha scritto:
> > fpu_activate hook is introduced by commit 6b52d186 (KVM: Activate fpu on
> > clts), however, there is no user currently, this patch drop it.
> >
> > Reviewed-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_host.h | 1 -
> >   arch/x86/kvm/svm.c              | 1 -
> >   arch/x86/kvm/vmx.c              | 1 -
> >   3 files changed, 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 5724601..b68f3e5 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -710,7 +710,6 @@ struct kvm_x86_ops {
> >   	void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
> >   	unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
> >   	void (*set_rflags)(struct kvm_vcpu *vcpu, unsigned long rflags);
> > -	void (*fpu_activate)(struct kvm_vcpu *vcpu);
> >   	void (*fpu_deactivate)(struct kvm_vcpu *vcpu);
> >   
> >   	void (*tlb_flush)(struct kvm_vcpu *vcpu);
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index ddf7427..1f49c86 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -4349,7 +4349,6 @@ static struct kvm_x86_ops svm_x86_ops = {
> >   	.cache_reg = svm_cache_reg,
> >   	.get_rflags = svm_get_rflags,
> >   	.set_rflags = svm_set_rflags,
> > -	.fpu_activate = svm_fpu_activate,
> >   	.fpu_deactivate = svm_fpu_deactivate,
> >   
> >   	.tlb_flush = svm_flush_tlb,
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 71cbee5..2963303 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -8896,7 +8896,6 @@ static struct kvm_x86_ops vmx_x86_ops = {
> >   	.cache_reg = vmx_cache_reg,
> >   	.get_rflags = vmx_get_rflags,
> >   	.set_rflags = vmx_set_rflags,
> > -	.fpu_activate = vmx_fpu_activate,
> >   	.fpu_deactivate = vmx_fpu_deactivate,
> >   
> >   	.tlb_flush = vmx_flush_tlb,
> Avi/Gleb, do you remember any particular reason for this?

IIRC (vaguely) if we expect the fpu to be used in the near future, we 
activate it eagerly so that we don't fault when it is used.

Prevents the sequence:

guest user: use fpu
#NM
host: reflect #NM to guest
guest kernel: CLTS
guest kernel: switch fpu state
#NM
host: switch fpu
guest kernel: switch fpu state (restarted)
guest user: use fpu (restarted)

Why was the user removed? Full-time eager fpu?
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