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

[Eric Northup]

On Sun, Sep 27, 2015 at 10:37 PM, Haozhong Zhang
<haozhong.zhang@xxxxxxxxx> 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 scaling 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.

reviewed-by: Eric Northup <digitaleric@xxxxxxxxxx>

>
> 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      |   4 +-
>  arch/x86/kvm/lapic.c            |   5 +-
>  arch/x86/kvm/svm.c              | 113 +++--------------------------
>  arch/x86/kvm/vmx.c              |  60 ++++++++--------
>  arch/x86/kvm/x86.c              | 154 +++++++++++++++++++++++++++++++++++++---
>  include/linux/kvm_host.h        |  21 +++++-
>  7 files changed, 221 insertions(+), 160 deletions(-)
>
> --
> 2.4.8
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/