Re: [PATCH v3] KVM: nVMX: Improve I/O exit handling

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-02-14 19:46, Jan Kiszka wrote:
> This prevents trapping L2 I/O exits if L1 has neither unconditional nor
> bitmap-based exiting enabled. Furthermore, it implements basic I/O
> bitmap handling. Repeated string accesses are still reported to L1
> unconditionally for now.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Changes in v3:
>  - trap unconditionally if bitmap access fails
> 
>  arch/x86/kvm/vmx.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 53 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6667042..2633199 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5908,6 +5908,58 @@ 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;
> +	bool string, rep;
> +	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;
> +
> +	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
> +
> +	string = exit_qualification & 16;
> +	rep = exit_qualification & 32;
> +
> +	/* TODO: interpret instruction and check range against bitmap */
> +	if (string && rep)
> +		return 1;

Nonsense, rep ins/outs always works against the same port. We can simply
drop this check and be done with the feature. I'll come up with v4.

Jan

> +
> +	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 +6149,7 @@ 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);
> 



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