Re: [PATCH 4/9] Implement GIF, clgi and stgi v3

[Joerg Roedel <joro@8bytes.org>]

I had another possible idea for performance improvement here. Since we
only inject normal interrupts and exceptions (and not NMI and such) we
can patch clgi to cli and stgi to sti to save these two intercepts in
the guests vmrun path.
Any objections/problems with this?

On Wed, Sep 17, 2008 at 03:41:21PM +0200, Alexander Graf wrote:
> This patch implements the GIF flag and the clgi and stgi instructions that
> set this flag. Only if the flag is set (default), interrupts can be received by
> the CPU.
> 
> To keep the information about that somewhere, this patch adds a new hidden
> flags vector. that is used to store information that does not go into the
> vmcb, but is SVM specific.
> 
> v2 moves the hflags to x86 generic code
> v3 makes use of the new permission helper
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  arch/x86/kvm/svm.c         |   42 +++++++++++++++++++++++++++++++++++++++---
>  include/asm-x86/kvm_host.h |    3 +++
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index c72e728..469ecc5 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -612,6 +612,8 @@ static void init_vmcb(struct vcpu_svm *svm)
>  		save->cr4 = 0;
>  	}
>  	force_new_asid(&svm->vcpu);
> +
> +	svm->vcpu.arch.hflags = HF_GIF_MASK;
>  }
>  
>  static int svm_vcpu_reset(struct kvm_vcpu *vcpu)
> @@ -1227,6 +1229,36 @@ static int nested_svm_do(struct vcpu_svm *svm,
>  	return retval;
>  }
>  
> +static int stgi_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> +{
> +	if (nested_svm_check_permissions(svm))
> +		return 1;
> +
> +	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
> +	skip_emulated_instruction(&svm->vcpu);
> +
> +	svm->vcpu.arch.hflags |= HF_GIF_MASK;
> +
> +	return 1;
> +}
> +
> +static int clgi_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> +{
> +	if (nested_svm_check_permissions(svm))
> +		return 1;
> +
> +	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
> +	skip_emulated_instruction(&svm->vcpu);
> +
> +	svm->vcpu.arch.hflags &= ~HF_GIF_MASK;
> +
> +	/* After a CLGI no interrupts should come */
> +	svm_clear_vintr(svm);
> +	svm->vmcb->control.int_ctl &= ~V_IRQ_MASK;
> +
> +	return 1;
> +}
> +
>  static int invalid_op_interception(struct vcpu_svm *svm,
>  				   struct kvm_run *kvm_run)
>  {
> @@ -1521,8 +1553,8 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm,
>  	[SVM_EXIT_VMMCALL]			= vmmcall_interception,
>  	[SVM_EXIT_VMLOAD]			= invalid_op_interception,
>  	[SVM_EXIT_VMSAVE]			= invalid_op_interception,
> -	[SVM_EXIT_STGI]				= invalid_op_interception,
> -	[SVM_EXIT_CLGI]				= invalid_op_interception,
> +	[SVM_EXIT_STGI]				= stgi_interception,
> +	[SVM_EXIT_CLGI]				= clgi_interception,
>  	[SVM_EXIT_SKINIT]			= invalid_op_interception,
>  	[SVM_EXIT_WBINVD]                       = emulate_on_interception,
>  	[SVM_EXIT_MONITOR]			= invalid_op_interception,
> @@ -1669,6 +1701,9 @@ static void svm_intr_assist(struct kvm_vcpu *vcpu)
>  	if (!kvm_cpu_has_interrupt(vcpu))
>  		goto out;
>  
> +	if (!(svm->vcpu.arch.hflags & HF_GIF_MASK))
> +		goto out;
> +
>  	if (!(vmcb->save.rflags & X86_EFLAGS_IF) ||
>  	    (vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK) ||
>  	    (vmcb->control.event_inj & SVM_EVTINJ_VALID)) {
> @@ -1720,7 +1755,8 @@ static void do_interrupt_requests(struct kvm_vcpu *vcpu,
>  
>  	svm->vcpu.arch.interrupt_window_open =
>  		(!(control->int_state & SVM_INTERRUPT_SHADOW_MASK) &&
> -		 (svm->vmcb->save.rflags & X86_EFLAGS_IF));
> +		 (svm->vmcb->save.rflags & X86_EFLAGS_IF) &&
> +		 (svm->vcpu.arch.hflags & HF_GIF_MASK));
>  
>  	if (svm->vcpu.arch.interrupt_window_open && svm->vcpu.arch.irq_summary)
>  		/*
> diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
> index 982b6b2..3e25004 100644
> --- a/include/asm-x86/kvm_host.h
> +++ b/include/asm-x86/kvm_host.h
> @@ -245,6 +245,7 @@ struct kvm_vcpu_arch {
>  	unsigned long cr3;
>  	unsigned long cr4;
>  	unsigned long cr8;
> +	u32 hflags;
>  	u64 pdptrs[4]; /* pae */
>  	u64 shadow_efer;
>  	u64 apic_base;
> @@ -734,6 +735,8 @@ enum {
>  	TASK_SWITCH_GATE = 3,
>  };
>  
> +#define HF_GIF_MASK		(1 << 0)
> +
>  /*
>   * Hardware virtualization extension instructions may fault if a
>   * reboot turns off virtualization while processes are running.
> -- 
> 1.5.6