Re: [PATCH] svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware

[Keir Fraser <keir.xen@gmail.com>]

On 20/04/2012 03:21, "Boris Ostrovsky" <boris.ostrovsky@amd.com> wrote:

> # HG changeset patch
> # User Boris Ostrovsky <boris.ostrovsky@amd.com>
> # Date 1334875170 14400
> # Node ID 55bf11ebce87ceb73fb2c372dcef170ec0bb4a18
> # Parent  7c777cb8f705411b77c551f34ba88bdc09e38ab8
> svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware
> 
> When running in TSC_MODE_ALWAYS_EMULATE mode on processors that support
> TSC scaling we don't need to intercept RDTSC/RDTSCP instructions.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
> Acked-by: Wei Huang <wei.huang2@amd.com>
> Tested-by: Wei Huang <wei.huang2@amd.com>

Worth an ack/nack from Dan M I'd say. He'll probably have some comment about
possible cross-CPU TSC skew.

 -- Keir

> diff -r 7c777cb8f705 -r 55bf11ebce87 xen/arch/x86/hvm/svm/svm.c
> --- a/xen/arch/x86/hvm/svm/svm.c Wed Apr 18 16:49:55 2012 +0100
> +++ b/xen/arch/x86/hvm/svm/svm.c Thu Apr 19 18:39:30 2012 -0400
> @@ -724,12 +724,18 @@ static void svm_set_rdtsc_exiting(struct
>  {
>      struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
>      u32 general1_intercepts = vmcb_get_general1_intercepts(vmcb);
> +    u32 general2_intercepts = vmcb_get_general2_intercepts(vmcb);
>  
>      general1_intercepts &= ~GENERAL1_INTERCEPT_RDTSC;
> -    if ( enable )
> +    general2_intercepts &= ~GENERAL2_INTERCEPT_RDTSCP;
> +
> +    if ( enable && !cpu_has_tsc_ratio ) {
>          general1_intercepts |= GENERAL1_INTERCEPT_RDTSC;
> +        general2_intercepts |= GENERAL2_INTERCEPT_RDTSCP;
> +    }
>  
>      vmcb_set_general1_intercepts(vmcb, general1_intercepts);
> +    vmcb_set_general2_intercepts(vmcb, general2_intercepts);
>  }
>  
>  static unsigned int svm_get_insn_bytes(struct vcpu *v, uint8_t *buf)
>