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

From: Paolo Bonzini
Date: Fri Nov 06 2015 - 05:49:20 EST




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

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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