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

[Haozhong Zhang]

On 11/06/15 11:49, Paolo Bonzini wrote:
> 
> 
> 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@xxxxxxxxxx>
> 
> 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
>
Agree

> 2) things that you are adding to include/linux/kvm_host.h should instead
> go in arch/x86/include/linux/kvm_host.h
>
Agree, because they are x86 specific.

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

Thanks,
Haozhong

> 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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