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

["Zhang, Haozhong" <haozhong.zhang@xxxxxxxxx>]

On 12/10/15 18:27, Tian, Kevin wrote:
> > 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...
>

The intention here is to fall back to the default ratio so that it
would work like no TSC scaling is used. However, I forgot here to fall
back v->domain->arch.tsc_khz and others to default values (i.e. values
used when no TSC scaling). I'll add them in the next version.

Haozhong

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