Re: [PATCH v3] kvm/fpu: Enable fully eager restore kvm FPU

[Avi Kivity <avi@redhat.com>]

On 09/12/2012 11:10 AM, Xudong Hao wrote:
> Enable KVM FPU fully eager restore, if there is other FPU state which isn't
> tracked by CR0.TS bit.
> 
> v3 changes from v2:
> - Make fpu active explicitly while guest xsave is enabling and non-lazy xstate bit
> exist.
> 
> v2 changes from v1:
> - Expand KVM_XSTATE_LAZY to 64 bits before negating it.
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 248c2b4..853e875 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3028,6 +3028,8 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>  
>  	if (!vcpu->fpu_active)
>  		hw_cr0 |= X86_CR0_TS | X86_CR0_MP;
> +	else
> +		hw_cr0 &= ~(X86_CR0_TS | X86_CR0_MP);
>  

Why?  The guest may wish to receive #NM faults.

>  	vmcs_writel(CR0_READ_SHADOW, cr0);
>  	vmcs_writel(GUEST_CR0, hw_cr0);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 20f2266..183cf60 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -560,6 +560,8 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>  		return 1;
>  	if (xcr0 & ~host_xcr0)
>  		return 1;
> +	if (xcr0 & ~((u64)KVM_XSTATE_LAZY))
> +		vcpu->fpu_active = 1;
>  	vcpu->arch.xcr0 = xcr0;
>  	vcpu->guest_xcr0_loaded = 0;
>  	return 0;
> @@ -5969,7 +5971,18 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
>  	vcpu->guest_fpu_loaded = 0;
>  	fpu_save_init(&vcpu->arch.guest_fpu);
>  	++vcpu->stat.fpu_reload;
> -	kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
> +	/*
> +	 * Currently KVM trigger FPU restore by #NM (via CR0.TS),
> +	 * till now only XCR0.bit0, XCR0.bit1, XCR0.bit2 is tracked

"currently", "till now", don't tell someone reading the code in six
months anything.  Just say how the code works.

> +	 * by TS bit, there might be other FPU state is not tracked
> +	 * by TS bit. Here it only make FPU deactivate request and do 
> +	 * FPU lazy restore for these cases: 1)xsave isn't enabled 
> +	 * in guest, 2)all guest FPU states can be tracked by TS bit.
> +	 * For others, doing fully FPU eager restore.
> +	 */
> +	if (!kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) ||
> +		!(vcpu->arch.xcr0 & ~((u64)KVM_XSTATE_LAZY)))
> +		kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
>  	trace_kvm_fpu(0);
>  }
>  
> 


-- 
error compiling committee.c: too many arguments to function