Re: [PATCH 2/5] kvm/svm: enhance MOV CR intercept handler

[Marcelo Tosatti <mtosatti@redhat.com>]

On Fri, Dec 10, 2010 at 02:51:25PM +0100, Andre Przywara wrote:
> Newer SVM implementations provide the GPR number in the VMCB, so
> that the emulation path is no longer necesarry to handle CR
> register access intercepts. Implement the handling in svm.c and
> use it when the info is provided.
> 
> Signed-off-by: Andre Przywara <andre.przywara@amd.com>
> ---
>  arch/x86/include/asm/svm.h |    2 +
>  arch/x86/kvm/svm.c         |   91 ++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 82 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 11dbca7..589fc25 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -256,6 +256,8 @@ struct __attribute__ ((__packed__)) vmcb {
>  #define SVM_EXITINFOSHIFT_TS_REASON_JMP 38
>  #define SVM_EXITINFOSHIFT_TS_HAS_ERROR_CODE 44
>  
> +#define SVM_EXITINFO_REG_MASK 0x0F
> +
>  #define	SVM_EXIT_READ_CR0 	0x000
>  #define	SVM_EXIT_READ_CR3 	0x003
>  #define	SVM_EXIT_READ_CR4 	0x004
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 298ff79..ee5f100 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -2594,12 +2594,81 @@ static int emulate_on_interception(struct vcpu_svm *svm)
>  	return emulate_instruction(&svm->vcpu, 0, 0, 0) == EMULATE_DONE;
>  }
>  
> +static int cr_interception(struct vcpu_svm *svm)
> +{
> +	int reg, cr;
> +	unsigned long val;
> +	int err;
> +
> +	if (!static_cpu_has(X86_FEATURE_DECODEASSISTS))
> +		return emulate_on_interception(svm);
> +
> +	/* bit 63 is the valid bit, as not all instructions (like lmsw)
> +	   provide the information */
> +	if (unlikely((svm->vmcb->control.exit_info_1 & (1ULL << 63)) == 0))
> +		return emulate_on_interception(svm);
> +
> +	reg = svm->vmcb->control.exit_info_1 & SVM_EXITINFO_REG_MASK;
> +	cr = svm->vmcb->control.exit_code - SVM_EXIT_READ_CR0;
> +
> +	err = 0;
> +	if (cr >= 16) { /* mov to cr */
> +		cr -= 16;
> +		val = kvm_register_read(&svm->vcpu, reg);
> +		switch (cr) {
> +		case 0:
> +			err = kvm_set_cr0(&svm->vcpu, val);
> +			break;
> +		case 3:
> +			err = kvm_set_cr3(&svm->vcpu, val);
> +			break;
> +		case 4:
> +			err = kvm_set_cr4(&svm->vcpu, val);
> +			break;
> +		case 8:
> +			err = kvm_set_cr8(&svm->vcpu, val);
> +			break;
> +		default:
> +			WARN(1, "unhandled write to CR%d", cr);
> +			return EMULATE_FAIL;
> +		}

Wrong return value? Is WARN() really wanted?