Re: [PATCH 3/24] Implement VMXON and VMXOFF

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sun, Jun 13, 2010 at 03:24:06PM +0300, Nadav Har'El wrote:
> This patch allows a guest to use the VMXON and VMXOFF instructions, and
> emulates them accordingly. Basically this amounts to checking some
> prerequisites, and then remembering whether the guest has enabled or disabled
> VMX operation.
> 
> Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
> ---
> --- .before/arch/x86/kvm/vmx.c	2010-06-13 15:01:28.000000000 +0300
> +++ .after/arch/x86/kvm/vmx.c	2010-06-13 15:01:28.000000000 +0300
> @@ -117,6 +117,16 @@ struct shared_msr_entry {
>  	u64 mask;
>  };
>  
> +/* The nested_vmx structure is part of vcpu_vmx, and holds information we need
> + * for correct emulation of VMX (i.e., nested VMX) on this vcpu. For example,
> + * the current VMCS set by L1, a list of the VMCSs used to run the active
> + * L2 guests on the hardware, and more.
> + */
> +struct nested_vmx {
> +	/* Has the level1 guest done vmxon? */
> +	bool vmxon;
> +};
> +
>  struct vcpu_vmx {
>  	struct kvm_vcpu       vcpu;
>  	struct list_head      local_vcpus_link;
> @@ -168,6 +178,9 @@ struct vcpu_vmx {
>  	u32 exit_reason;
>  
>  	bool rdtscp_enabled;
> +
> +	/* Support for guest hypervisors (nested VMX) */
> +	struct nested_vmx nested;
>  };
>  
>  static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
> @@ -3353,6 +3366,93 @@ static int handle_vmx_insn(struct kvm_vc
>  	return 1;
>  }
>  
> +/* Emulate the VMXON instruction.
> + * Currently, we just remember that VMX is active, and do not save or even
> + * inspect the argument to VMXON (the so-called "VMXON pointer") because we
> + * do not currently need to store anything in that guest-allocated memory
> + * region. Consequently, VMCLEAR and VMPTRLD also do not verify that the their
> + * argument is different from the VMXON pointer (which the spec says they do).
> + */
> +static int handle_vmon(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_segment cs;
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> +	/* The Intel VMX Instruction Reference lists a bunch of bits that
> +	 * are prerequisite to running VMXON, most notably CR4.VMXE must be
> +	 * set to 1. Otherwise, we should fail with #UD. We test these now:
> +	 */
> +	if (!nested) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 1;
> +	}
> +
> +	if (!(vcpu->arch.cr4 & X86_CR4_VMXE) ||
> +	    !(vcpu->arch.cr0 & X86_CR0_PE) ||

kvm_read_cr0_bits, kvm_read_cr4_bits.