Re: [PATCH] KVM: VMX: enable acknowledge interupt on vmexit

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jan 16, 2013 at 05:00:48PM +0800, Yang Zhang wrote:
> From: Yang Zhang <yang.z.zhang@Intel.com>
> 
> The "acknowledge interrupt on exit" feature controls processor behavior
> for external interrupt acknowledgement. When this control is set, the
> processor acknowledges the interrupt controller to acquire the
> interrupt vector on VM exit.
> 
> This feature is required by Posted Interrupt. It will be turnned on only
> when posted interrupt is enabled.
> 
Why? Always enable it. It is faster than current approach.

> Refer to Intel SDM volum 3, chapter 33.2.
> 
Please CC H. Peter Anvin <hpa@linux.intel.com> on the next version.

> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> ---
>  arch/x86/kvm/vmx.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index dd2a85c..d1ed9ae 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2565,7 +2565,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>  #ifdef CONFIG_X86_64
>  	min |= VM_EXIT_HOST_ADDR_SPACE_SIZE;
>  #endif
> -	opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT;
> +	opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT | VM_EXIT_ACK_INTR_ON_EXIT;
>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
>  				&_vmexit_control) < 0)
>  		return -EIO;
> @@ -3926,7 +3926,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
>  		++vmx->nmsrs;
>  	}
>  
> -	vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
> +	vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl & ~VM_EXIT_ACK_INTR_ON_EXIT);
>  
>  	/* 22.2.1, 20.8.1 */
>  	vmcs_write32(VM_ENTRY_CONTROLS, vmcs_config.vmentry_ctrl);
> @@ -6096,6 +6096,52 @@ static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
>  	}
>  }
>  
> +
> +static noinline void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
> +{
> +	u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
> +
> +	if ((exit_intr_info & INTR_INFO_INTR_TYPE_MASK) == INTR_TYPE_EXT_INTR &&
> +	    (exit_intr_info & INTR_INFO_VALID_MASK) ) {
if (exit_intr_info & (INTR_INFO_VALID_MASK | INTR_INFO_INTR_TYPE_MASK)
== (INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR))

> +		unsigned int vector;
> +		unsigned long entry;
> +		struct desc_ptr dt;
> +		gate_desc *desc;
> +
> +		native_store_idt(&dt);
This does not change. Store it in vcpu during vcpu creation instead of
reading it each time.

> +
> +		vector =  exit_intr_info & INTR_INFO_VECTOR_MASK;
> +		desc = (void *)dt.address + vector * 16;
> +
> +		entry = gate_offset(*desc);
> +		asm(
> +			"mov %0, %%" _ASM_DX "\n\t"
> +			"mov %%" _ASM_SP ", %%" _ASM_BX "\n\t"
> +#ifdef CONFIG_X86_64
> +			"and $0xfffffffffffffff0, %%" _ASM_SP "\n\t"
> +#endif
> +			"mov %%ss, %%" _ASM_AX "\n\t"
> +			"push %%" _ASM_AX "\n\t"
> +			"push %%" _ASM_BX "\n\t"
For 32bit you do not need to save ss:esp.

> +			"pushf\n\t"
> +			"mov %%cs, %%" _ASM_AX "\n\t"
> +			"push %%" _ASM_AX "\n\t"
> +			"push intr_return\n\t"
> +			"jmp *%% " _ASM_DX "\n\t"
> +			".pushsection .rodata \n\t"
> +			".global intr_return \n\t"
> +			"intr_return: " _ASM_PTR " 1b \n\t"
> +			".popsection\n\t"
> +			: :"m"(entry) : 
> +#ifdef CONFIG_X86_64
> +			"rax", "rbx", "rdx"
> +#else
> +			"eax", "ebx", "edx"
> +#endif
> +			);
> +	}
> +}
> +
>  static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
>  {
>  	u32 exit_intr_info;
> @@ -6431,6 +6477,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	vmx_complete_atomic_exit(vmx);
>  	vmx_recover_nmi_blocking(vmx);
>  	vmx_complete_interrupts(vmx);
> +	vmx_handle_external_intr(vcpu);
This should be done just before enabling interrupts, otherwise we are
taking an interrupt before vmexit is fully complete.

--
			Gleb.