Re: [PATCH v7] KVM: VMX: Enable XSAVE/XRSTOR for guest

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, May 31, 2010 at 07:54:11PM +0800, Sheng Yang wrote:
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 99ae513..8649627 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -36,6 +36,8 @@
>  #include <asm/vmx.h>
>  #include <asm/virtext.h>
>  #include <asm/mce.h>
> +#include <asm/i387.h>
> +#include <asm/xcr.h>
>  
>  #include "trace.h"
>  
> @@ -3354,6 +3356,16 @@ static int handle_wbinvd(struct kvm_vcpu *vcpu)
>  	return 1;
>  }
>  
> +static int handle_xsetbv(struct kvm_vcpu *vcpu)
> +{
> +	u64 new_bv = kvm_read_edx_eax(vcpu);
> +	u32 index = kvm_register_read(vcpu, VCPU_REGS_RCX);
> +
> +	kvm_set_xcr(vcpu, index, new_bv);
> +	skip_emulated_instruction(vcpu);

Should only skip_emulated_instruction if no exception was injected.

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7be1d36..0fcd8de 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c

> +int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
> +{
> +	u64 xcr0;
> +
> +	/* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
> +	if (index != XCR_XFEATURE_ENABLED_MASK)
> +		return 1;
> +	xcr0 = xcr;
> +	if (kvm_x86_ops->get_cpl(vcpu) != 0)
> +		return 1;
> +	if (!(xcr0 & XSTATE_FP))
> +		return 1;
> +	if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
> +		return 1;
> +	if (xcr0 & ~host_xcr0)
> +		return 1;
> +	vcpu->arch.xcr0 = xcr0;
> +	xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);

Won't this happen on guest entry, since vcpu->guest_xcr0_loaded == 0?

> @@ -4522,6 +4602,24 @@ static void inject_pending_event(struct kvm_vcpu *vcpu)
>  	}
>  }
>  
> +static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
> +{
> +	if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
> +			!vcpu->guest_xcr0_loaded) {
> +		xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);

Only necessary if guest and hosts XCR0 differ?

> +		vcpu->guest_xcr0_loaded = 1;
> +	}
> +}
> +
> +static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
> +{
> +	if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
> +			vcpu->guest_xcr0_loaded) {
> +		xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
> +		vcpu->guest_xcr0_loaded = 0;
> +	}
> +}

What if you load guest's XCR0, then guest clears CR4.OSXSAVE? (restore 
of host_xcr0 should be conditional on guest_xcr0_loaded only).

> +
>  static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  {
>  	int r;
> @@ -4567,6 +4665,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	kvm_x86_ops->prepare_guest_switch(vcpu);
>  	if (vcpu->fpu_active)
>  		kvm_load_guest_fpu(vcpu);
> +	kvm_load_guest_xcr0(vcpu);
>  
>  	atomic_set(&vcpu->guest_mode, 1);
>  	smp_wmb();
> @@ -5118,6 +5217,11 @@ void fx_init(struct kvm_vcpu *vcpu)
>  	fpu_alloc(&vcpu->arch.guest_fpu);
>  	fpu_finit(&vcpu->arch.guest_fpu);
>  
> +	/*
> +	 * Ensure guest xcr0 is valid for loading
> +	 */
> +	vcpu->arch.xcr0 = XSTATE_FP;
> +
>  	vcpu->arch.cr0 |= X86_CR0_ET;
>  }
>  EXPORT_SYMBOL_GPL(fx_init);
> @@ -5132,6 +5236,12 @@ void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
>  	if (vcpu->guest_fpu_loaded)
>  		return;
>  
> +	/*
> +	 * Restore all possible states in the guest,
> +	 * and assume host would use all available bits.
> +	 * Guest xcr0 would be loaded later.
> +	 */
> +	kvm_put_guest_xcr0(vcpu);
>  	vcpu->guest_fpu_loaded = 1;
>  	unlazy_fpu(current);
>  	fpu_restore_checking(&vcpu->arch.guest_fpu);
> @@ -5140,6 +5250,8 @@ void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
>  
>  void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
> {
> +	kvm_put_guest_xcr0(vcpu);
> +

Should be in kvm_arch_vcpu_put?

>  	if (!vcpu->guest_fpu_loaded)
>  		return;
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 4e8fdbf..3784d58 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -88,7 +88,7 @@ struct kvm_vcpu {
>  	int srcu_idx;
>  
>  	int fpu_active;
> -	int guest_fpu_loaded;
> +	int guest_fpu_loaded, guest_xcr0_loaded;
>  	wait_queue_head_t wq;
>  	int sigset_active;
>  	sigset_t sigset;
> -- 
> 1.7.0.1
> 
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