Re: [PATCH v5] KVM: nVMX: Improve I/O exit handling

[Gleb Natapov <gleb@redhat.com>]

On Mon, Feb 18, 2013 at 10:17:14AM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> This prevents trapping L2 I/O exits if L1 has neither unconditional nor
> bitmap-based exiting enabled. Furthermore, it implements I/O bitmap
> handling. We still exit unconditionally in case the CPU does not provide
> information for ins/outs.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Changes in v5:
>  - still exit unconditionally if CPU refuses to provide exit
>    information on ins/outs
> 
>  arch/x86/kvm/vmx.c |   58 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 56 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6667042..ccc7c17 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -651,6 +651,7 @@ static struct vmcs_config {
>  	int size;
>  	int order;
>  	u32 revision_id;
> +	u32 vmx_basic_high;
>  	u32 pin_based_exec_ctrl;
>  	u32 cpu_based_exec_ctrl;
>  	u32 cpu_based_2nd_exec_ctrl;
> @@ -752,6 +753,11 @@ static inline bool vm_need_tpr_shadow(struct kvm *kvm)
>  	return (cpu_has_vmx_tpr_shadow()) && (irqchip_in_kernel(kvm));
>  }
>  
> +static inline bool cpu_has_stringio_exit_info(void)
> +{
> +	return vmcs_config.vmx_basic_high & (VMX_BASIC_INOUT >> 32);
> +}
> +
>  static inline bool cpu_has_secondary_exec_ctrls(void)
>  {
>  	return vmcs_config.cpu_based_exec_ctrl &
> @@ -2635,6 +2641,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>  	vmcs_conf->size = vmx_msr_high & 0x1fff;
>  	vmcs_conf->order = get_order(vmcs_config.size);
>  	vmcs_conf->revision_id = vmx_msr_low;
> +	vmcs_conf->vmx_basic_high = vmx_msr_high;
>  
>  	vmcs_conf->pin_based_exec_ctrl = _pin_based_exec_control;
>  	vmcs_conf->cpu_based_exec_ctrl = _cpu_based_exec_control;
> @@ -5908,6 +5915,54 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
>  static const int kvm_vmx_max_exit_handlers =
>  	ARRAY_SIZE(kvm_vmx_exit_handlers);
>  
> +static bool nested_vmx_exit_handled_io(struct kvm_vcpu *vcpu,
> +				       struct vmcs12 *vmcs12)
> +{
> +	unsigned long exit_qualification;
> +	gpa_t bitmap, last_bitmap;
> +	u16 port;
> +	int size;
> +	u8 b;
> +
> +	if (nested_cpu_has(vmcs12, CPU_BASED_UNCOND_IO_EXITING))
> +		return 1;
> +
> +	if (!nested_cpu_has(vmcs12, CPU_BASED_USE_IO_BITMAPS))
> +		return 0;
> +
> +	/* TODO: for older CPUs, derive access width from instruction */
> +	if (!cpu_has_stringio_exit_info())
> +		return 1;
> +

Sigh, actually I am stupid :( The information that is not available
on older cpus is address size in "VM-exit instruction information",
not operand size on exit qualification, so your v4 is correct. Except
handling of port wrap around:

  If the “use I/O bitmaps” VM-execution control is 1, the instruction
  causes a VM exit if it attempts to access an I/O port corresponding to a
  bit set to 1 in the appropriate I/O bitmap (see Section 24.6.4). If an
  I/O operation “wraps around” the 16-bit I/O-port space (accesses
  ports FFFFH and 0000H), the I/O instruction causes a VM exit (the
  “unconditional I/O exiting” VM-execution control is ignored if the
  “use I/O bitmaps” VM-execution control is 1).


> +	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
> +
> +	port = exit_qualification >> 16;
> +	size = (exit_qualification & 7) + 1;
> +
> +	last_bitmap = (gpa_t)-1;
> +	b = -1;
> +
> +	while (size > 0) {
> +		if (port < 0x8000)
> +			bitmap = vmcs12->io_bitmap_a;
> +		else
> +			bitmap = vmcs12->io_bitmap_b;
> +		bitmap += (port & 0x7fff) / 8;
> +
> +		if (last_bitmap != bitmap)
> +			if (kvm_read_guest(vcpu->kvm, bitmap, &b, 1))
> +				return 1;
> +		if (b & (1 << (port & 7)))
> +			return 1;
> +
> +		port++;
> +		size--;
> +		last_bitmap = bitmap;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Return 1 if we should exit from L2 to L1 to handle an MSR access access,
>   * rather than handle it ourselves in L0. I.e., check whether L1 expressed
> @@ -6097,8 +6152,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
>  	case EXIT_REASON_DR_ACCESS:
>  		return nested_cpu_has(vmcs12, CPU_BASED_MOV_DR_EXITING);
>  	case EXIT_REASON_IO_INSTRUCTION:
> -		/* TODO: support IO bitmaps */
> -		return 1;
> +		return nested_vmx_exit_handled_io(vcpu, vmcs12);
>  	case EXIT_REASON_MSR_READ:
>  	case EXIT_REASON_MSR_WRITE:
>  		return nested_vmx_exit_handled_msr(vcpu, vmcs12, exit_reason);
> -- 
> 1.7.3.4

--
			Gleb.