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

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Date:	Mon, 28 Sep 2015 20:28:57 -0700
From:	Eric Northup <digitaleric@...gle.com>
To:	Haozhong Zhang <haozhong.zhang@...el.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 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.

>
>  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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