Re: [Qemu-devel] [PATCH v2 0/3] x86-kvm: Fix Mac guest timekeeping by exposing TSC frequency in CPUID

[Paolo Bonzini]

On 20/01/2017 15:11, Phil Dennis-Jordan wrote:
> Darwin/OS X/macOS for x86-64 uses the TSC for timekeeping; it normally 
> calibrates this by querying various clock frequency scaling MSRs. Details 
> depend on the exact CPU model detected. The local APIC timer frequency is 
> extracted from (EFI) firmware. Virtualisation environments including Qemu/KVM 
> don't expose those MSRs to guests, and in any case the host and guest CPUs' 
> MSRs may not match up. To solve this, the xnu kernel queries CPUID leaf 
> 0x40000010 for the TSC and APIC timers if leaf 0x40000000 suggests that this 
> leaf exists, which is the case when running inside VMWare (Fusion). This 
> patch series replicates the behaviour of these CPUID leaves for Qemu/KVM via 
> a new x86 CPU option, "vmware-cpuid-freq."
> 
> The option is activated by default on 2.9 and newer pc (PIIX and Q35) machine 
> variants, if the TSC is stable and known (invtsc or user-specified).
> 
> Changelog
> ========
> 
> v1 -> v2
>  * The v1 thread was "[PATCH] x86-KVM: Supply TSC and APIC clock rates to 
> guest like VMWare"
>  * The option has been renamed as suggested in the v1 discussion.
>  * It now checks that either invtsc or a user-specified TSC clock rate are 
> active before activating leaf 0x40000010.
>  * CPUID leaf 0x40000000 exposed by KVM will only reference 0x40000010 if all 
> preconditions are met and the functionality is actually active.
>  * No more error message if preconditions are not met.
>  * cpuid_data.cpuid.nent update/cpuid_find_entry bug fixed.
>  * 2 extra patches included, one for setting up PC machine version 2.8/2.9 
> compatibility configurations, the second for enabling the new option in 
> version 2.9+ PIIX/q35 configurations by default, while leaving it disabled 
> for 2.8 or older machines.
> 
> Phil Dennis-Jordan (3):
>   x86-KVM: Supply TSC and APIC clock rates to guest like VMWare
>   pc: Add 2.9 machine type
>   pc: Enable vmware-cpuid-freq CPU option for 2.9+ machine types
> 
>  hw/i386/pc_piix.c    | 13 ++++++++++++-
>  hw/i386/pc_q35.c     | 12 +++++++++++-
>  include/hw/i386/pc.h |  6 ++++++
>  target/i386/cpu.c    |  1 +
>  target/i386/cpu.h    |  4 ++++
>  target/i386/kvm.c    | 36 ++++++++++++++++++++++++++++++------
>  6 files changed, 64 insertions(+), 8 deletions(-)
> 

Looks good, thanks!  Queued patches 1 and 3 for 2.9 (patch 2 is in already).

Paolo