Re: [Xen-devel] [PATCH v2 09/14] x86/hvm: Setup TSC scaling ratio

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Zhang, Haozhong
> Sent: Monday, December 07, 2015 4:59 AM
> 
> This patch adds a field tsc_scaling_ratio in struct hvm_vcpu to
> record the TSC scaling ratio, and sets it up when tsc_set_info() is
> called for a vcpu or when a vcpu is restored or reset.
> 
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> ---
>  xen/arch/x86/hvm/hvm.c            | 30
> ++++++++++++++++++++++++++++++
>  xen/arch/x86/hvm/svm/svm.c        |  6 ++++--
>  xen/arch/x86/time.c               | 13 ++++++++++++-
>  xen/include/asm-x86/hvm/hvm.h     |  5 +++++
>  xen/include/asm-x86/hvm/svm/svm.h |  3 ---
>  xen/include/asm-x86/hvm/vcpu.h    |  2 ++
>  xen/include/asm-x86/math64.h      | 30
> ++++++++++++++++++++++++++++++
>  7 files changed, 83 insertions(+), 6 deletions(-)
>  create mode 100644 xen/include/asm-x86/math64.h
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 0e63c33..52a0ef8 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -65,6 +65,7 @@
>  #include <asm/mtrr.h>
>  #include <asm/apic.h>
>  #include <asm/vm_event.h>
> +#include <asm/math64.h>
>  #include <public/sched.h>
>  #include <public/hvm/ioreq.h>
>  #include <public/version.h>
> @@ -301,6 +302,29 @@ int hvm_set_guest_pat(struct vcpu *v, u64 guest_pat)
>      return 1;
>  }
> 
> +void hvm_setup_tsc_scaling(struct vcpu *v)
> +{
> +    u64 ratio;
> +
> +    if ( !hvm_funcs.tsc_scaling_supported )
> +        return;
> +
> +    /*
> +     * The multiplication of the first two terms may overflow a 64-bit
> +     * integer, so use mul_u64_u32_div() instead to keep precision.
> +     */
> +    ratio = mul_u64_u32_div(1ULL << hvm_funcs.tsc_scaling_ratio_frac_bits,
> +                            v->domain->arch.tsc_khz, cpu_khz);
> +
> +    if ( ratio == 0 || ratio > hvm_funcs.max_tsc_scaling_ratio )
> +        return;

How will you check such error in other places? tsc_scaling_ratio is
left w/ default value, while if you don't detect the issue that that
ratio will be used for wrong scale...

Thanks
Kevin

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