linux-kernel - Re: [PATCH v2 00/12] KVM: x86: add support for VMX TSC scaling

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Date:	Fri, 6 Nov 2015 11:49:08 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Haozhong Zhang <haozhong.zhang@...el.com>, kvm@...r.kernel.org
Cc:	Gleb Natapov <gleb@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Joerg Roedel <joro@...tes.org>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	mdontu@...defender.com, Kai Huang <kai.huang@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/12] KVM: x86: add support for VMX TSC scaling



On 20/10/2015 09:39, Haozhong Zhang wrote:
> This patchset adds support for VMX TSC scaling feature which is
> available on Intel Skylake CPU. The specification of VMX TSC scaling
> can be found at
> http://www.intel.com/content/www/us/en/processors/timestamp-counter-scaling-virtualization-white-paper.html
> 
> VMX TSC scaling allows guest TSC which is read by guest rdtsc(p)
> instructions increases in a rate that is customized by the hypervisor
> and can be different than the host TSC rate. Basically, VMX TSC
> scaling adds a 64-bit field called TSC multiplier in VMCS so that, if
> VMX TSC scaling is enabled, TSC read by guest rdtsc(p) instructions
> will be calculated by the following formula:
> 
>   guest EDX:EAX = (Host TSC * TSC multiplier) >> 48 + VMX TSC Offset
> 
> where, Host TSC = Host MSR_IA32_TSC + Host MSR_IA32_TSC_ADJUST.
> 
> This patchset, when cooperating with another QEMU patchset (sent in
> another email "target-i386: save/restore vcpu's TSC rate during
> migration"), allows guest programs observe a consistent TSC rate even
> though they are migrated among machines with different host TSC rates.
> 
> VMX TSC scaling shares some common logics with SVM TSC ratio which
> is already supported by KVM. Patch 1 ~ 8 move those common logics from
> SVM code to the common code. Upon them, patch 9 ~ 12 add VMX-specific
> support for VMX TSC scaling.
> 
> Changes in v2:
>  * Remove the duplicated variable 'kvm_tsc_scaling_ratio_rsvd'.
>  * Remove an unnecessary error check in original patch 2.
>  * Do 64-bit arithmetic by functions recommended by Paolo.
>  * Make kvm_set_tsc_khz() returns an error number so that ioctl
>    KVM_SET_TSC_KHZ does not return 0 if errors happen.
> 
> Reviewed-by: Eric Northup <digitaleric@...gle.com>

Thanks for the patches.  There are a couple changes that I can do myself:

1) kvm_default_tsc_scaling_ratio can be initialized in
kvm_arch_hardware_setup, since it's just 1ULL <<
kvm_tsc_scaling_ratio_frac_bits

2) things that you are adding to include/linux/kvm_host.h should instead
go in arch/x86/include/linux/kvm_host.h

That's it.  I'll commit it as soon as I test on AMD (today hopefully).

Paolo

> Haozhong Zhang (12):
>   KVM: x86: Collect information for setting TSC scaling ratio
>   KVM: x86: Add a common TSC scaling ratio field in kvm_vcpu_arch
>   KVM: x86: Add a common TSC scaling function
>   KVM: x86: Replace call-back set_tsc_khz() with a common function
>   KVM: x86: Replace call-back compute_tsc_offset() with a common function
>   KVM: x86: Move TSC scaling logic out of call-back adjust_tsc_offset()
>   KVM: x86: Move TSC scaling logic out of call-back read_l1_tsc()
>   KVM: x86: Use the correct vcpu's TSC rate to compute time scale
>   KVM: VMX: Enable and initialize VMX TSC scaling
>   KVM: VMX: Setup TSC scaling ratio when a vcpu is loaded
>   KVM: VMX: Use a scaled host TSC for guest readings of MSR_IA32_TSC
>   KVM: VMX: Dump TSC multiplier in dump_vmcs()
> 
>  arch/x86/include/asm/kvm_host.h |  24 +++----
>  arch/x86/include/asm/vmx.h      |   3 +
>  arch/x86/kvm/lapic.c            |   4 +-
>  arch/x86/kvm/svm.c              | 116 ++++------------------------------
>  arch/x86/kvm/vmx.c              |  64 ++++++++++---------
>  arch/x86/kvm/x86.c              | 134 +++++++++++++++++++++++++++++++++++-----
>  include/linux/kvm_host.h        |  20 ++++++
>  include/linux/math64.h          |  99 +++++++++++++++++++++++++++++
>  8 files changed, 297 insertions(+), 167 deletions(-)
> 
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