Re: [PATCH 7/24] Understanding guest pointers to vmcs12 structures

[Avi Kivity <avi@redhat.com>]

On 06/13/2010 03:26 PM, Nadav Har'El wrote:
> This patch includes a couple of utility functions for extracting pointer
> operands of VMX instructions issued by L1 (a guest hypervisor), and
> translating guest-given vmcs12 virtual addresses to guest-physical addresses.
>
> +/*
> + * Decode the memory-address operand of a vmx instruction, according to the
> + * Intel spec.
> + */
> +#define VMX_OPERAND_SCALING(vii)	((vii)&  3)
> +#define VMX_OPERAND_ADDR_SIZE(vii)	(((vii)>>  7)&  7)
> +#define VMX_OPERAND_IS_REG(vii)		((vii)&  (1u<<  10))
> +#define VMX_OPERAND_SEG_REG(vii)	(((vii)>>  15)&  7)
> +#define VMX_OPERAND_INDEX_REG(vii)	(((vii)>>  18)&  0xf)
> +#define VMX_OPERAND_INDEX_INVALID(vii)	((vii)&  (1u<<  22))
> +#define VMX_OPERAND_BASE_REG(vii)	(((vii)>>  23)&  0xf)
> +#define VMX_OPERAND_BASE_INVALID(vii)	((vii)&  (1u<<  27))
> +#define VMX_OPERAND_REG(vii)		(((vii)>>  3)&  0xf)
> +#define VMX_OPERAND_REG2(vii)		(((vii)>>  28)&  0xf)
> +static gva_t get_vmx_mem_address(struct kvm_vcpu *vcpu,
> +				 unsigned long exit_qualification,
> +				 u32 vmx_instruction_info)
> +{
> +	int  scaling = VMX_OPERAND_SCALING(vmx_instruction_info);
> +	int  addr_size = VMX_OPERAND_ADDR_SIZE(vmx_instruction_info);
> +	bool is_reg = VMX_OPERAND_IS_REG(vmx_instruction_info);
> +	int  seg_reg = VMX_OPERAND_SEG_REG(vmx_instruction_info);
> +	int  index_reg = VMX_OPERAND_SEG_REG(vmx_instruction_info);
> +	bool index_is_valid = !VMX_OPERAND_INDEX_INVALID(vmx_instruction_info);
> +	int  base_reg       = VMX_OPERAND_BASE_REG(vmx_instruction_info);
> +	bool base_is_valid  = !VMX_OPERAND_BASE_INVALID(vmx_instruction_info);
>    

Since those defines are used just ones, you can fold them into their 
uses.  It doesn't add much to repeat the variable name.

> +	gva_t addr;
> +
> +	if (is_reg) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 0;
> +	}
> +
> +	switch (addr_size) {
> +	case 1: /* 32 bit. high bits are undefined according to the spec: */
> +		exit_qualification&= 0xffffffff;
> +		break;
> +	case 2: /* 64 bit */
> +		break;
> +	default: /* addr_size=0 means 16 bit */
> +		return 0;
> +	}
> +
> +	/* Addr = segment_base + offset */
> +	/* offfset = Base + [Index * Scale] + Displacement */
> +	addr = vmx_get_segment_base(vcpu, seg_reg);
> +	if (base_is_valid)
> +		addr += kvm_register_read(vcpu, base_reg);
> +	if (index_is_valid)
> +		addr += kvm_register_read(vcpu, index_reg)<<scaling;
> +	addr += exit_qualification; /* holds the displacement */
>    

Do we need a segment limit and access rights check?

> +
> +	return addr;
> +}
> +
>    

-- 
error compiling committee.c: too many arguments to function