linux-kernel - Re: [PATCH 01/12] KVM: x86: Collect information for setting TSC scaling ratio

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Date:	Tue, 29 Sep 2015 12:01:17 +0800
From:	Haozhong Zhang <haozhong.zhang@...el.com>
To:	Eric Northup <digitaleric@...gle.com>
Cc:	KVM <kvm@...r.kernel.org>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Joerg Roedel <joro@...tes.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Mihai Donțu <mdontu@...defender.com>,
	Andy Lutomirski <luto@...nel.org>,
	Kai Huang <kai.huang@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/12] KVM: x86: Collect information for setting TSC
 scaling ratio

On Mon, Sep 28, 2015 at 08:28:57PM -0700, Eric Northup wrote:
> On Sun, Sep 27, 2015 at 10:38 PM, Haozhong Zhang
> <haozhong.zhang@...el.com> wrote:
> >
> > The number of bits of the fractional part of the 64-bit TSC scaling
> > ratio in VMX and SVM is different. This patch makes the architecture
> > code to collect the number of fractional bits and other related
> > information into variables that can be accessed in the common code.
> >
> > Signed-off-by: Haozhong Zhang <haozhong.zhang@...el.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h | 8 ++++++++
> >  arch/x86/kvm/svm.c              | 5 +++++
> >  arch/x86/kvm/x86.c              | 8 ++++++++
> >  3 files changed, 21 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 2beee03..5b9b86e 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -965,6 +965,14 @@ extern bool kvm_has_tsc_control;
> >  extern u32  kvm_min_guest_tsc_khz;
> >  /* maximum supported tsc_khz for guests */
> >  extern u32  kvm_max_guest_tsc_khz;
> > +/* number of bits of the fractional part of the TSC scaling ratio */
> > +extern u8   kvm_tsc_scaling_ratio_frac_bits;
> > +/* reserved bits of TSC scaling ratio (SBZ) */
> > +extern u64  kvm_tsc_scaling_ratio_rsvd;
> > +/* default TSC scaling ratio (= 1.0) */
> > +extern u64  kvm_default_tsc_scaling_ratio;
> > +/* maximum allowed value of TSC scaling ratio */
> > +extern u64  kvm_max_tsc_scaling_ratio;
> 
> Do we need all 3 of kvm_max_guest_tsc_khz, kvm_max_tsc_scaling_ratio,
> and kvm_tsc_scaling_ratio_rsvd (since only SVM has reserved bits - and
> just for complaining if the high bits are set, which can already be
> expressed by max_tsc_scaling ratio)
> 
> kvm_max_tsc_scaling_ratio seems to be write-only.
>

You are right. I'll remove kvm_tsc_scaling_ratio_rsvd and just use
kvm_max_tsc_scaling_ratio to verify TSC scaling ratio in
set_tsc_khz().

> >
> >  enum emulation_result {
> >         EMULATE_DONE,         /* no further processing */
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index 94b7d15..eff7db7 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -963,7 +963,12 @@ static __init int svm_hardware_setup(void)
> >                 max = min(0x7fffffffULL, __scale_tsc(tsc_khz, TSC_RATIO_MAX));
> >
> >                 kvm_max_guest_tsc_khz = max;
> > +
> > +               kvm_max_tsc_scaling_ratio = TSC_RATIO_MAX;
> > +               kvm_tsc_scaling_ratio_frac_bits = 32;
> > +               kvm_tsc_scaling_ratio_rsvd = TSC_RATIO_RSVD;
> >         }
> > +       kvm_default_tsc_scaling_ratio = TSC_RATIO_DEFAULT;
> >
> >         if (nested) {
> >                 printk(KERN_INFO "kvm: Nested Virtualization enabled\n");
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 991466b..f888225 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -106,6 +106,14 @@ bool kvm_has_tsc_control;
> >  EXPORT_SYMBOL_GPL(kvm_has_tsc_control);
> >  u32  kvm_max_guest_tsc_khz;
> >  EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz);
> > +u8   kvm_tsc_scaling_ratio_frac_bits;
> > +EXPORT_SYMBOL_GPL(kvm_tsc_scaling_ratio_frac_bits);
> > +u64  kvm_tsc_scaling_ratio_rsvd;
> > +EXPORT_SYMBOL_GPL(kvm_tsc_scaling_ratio_rsvd);
> > +u64  kvm_default_tsc_scaling_ratio;
> > +EXPORT_SYMBOL_GPL(kvm_default_tsc_scaling_ratio);
> > +u64  kvm_max_tsc_scaling_ratio;
> > +EXPORT_SYMBOL_GPL(kvm_max_tsc_scaling_ratio);
> >
> >  /* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */
> >  static u32 tsc_tolerance_ppm = 250;
> > --
> > 2.4.8
> >
> > --
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