Re: [Qemu-devel] [PATCH] i386/cpu/hyperv: support over 64 vcpus for windows guests

[Gonglei (Arei)]

> -----Original Message-----
> From: Eduardo Habkost [mailto:address@hidden
> Sent: Tuesday, September 12, 2017 2:38 AM
> To: Gonglei (Arei)
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden;
> Huangweidong (C)
> Subject: Re: [PATCH] i386/cpu/hyperv: support over 64 vcpus for windows
> guests
> 
> On Mon, Sep 11, 2017 at 11:20:27PM +0800, Gonglei wrote:
> > Starting with Windows Server 2012 and Windows 8, if
> > CPUID.40000005.EAX contains a value of -1, Windows assumes specific
> > limit to the number of VPs. In this case, Windows Server 2012
> > guest VMs may use more than 64 VPs, up to the maximum supported
> > number of processors applicable to the specific Windows
> > version being used.
> >
> >
> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/referenc
> e/tlfs
> >
> > For compatibility, Let's introduce a new property for X86CPU,
> > named "x-hv-max-vps" as Eduardo's suggestion, and set it
> > to 0x40 before machine 2.10.
> >
> > (The "x-" prefix indicates that the property is not supposed to
> > be a stable user interface.)
> >
> > Signed-off-by: Gonglei <address@hidden>
> > ---
> >  include/hw/i386/pc.h |  5 +++++
> >  target/i386/cpu.c    |  1 +
> >  target/i386/cpu.h    |  2 ++
> >  target/i386/kvm.c    | 15 ++++++++++++++-
> >  4 files changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > index 8226904..087d184 100644
> > --- a/include/hw/i386/pc.h
> > +++ b/include/hw/i386/pc.h
> > @@ -371,6 +371,11 @@ bool e820_get_entry(int, uint32_t, uint64_t *,
> uint64_t *);
> >
> >  #define PC_COMPAT_2_10 \
> >      HW_COMPAT_2_10 \
> > +    {\
> > +        .driver   = TYPE_X86_CPU,\
> > +        .property = "x-hv-max-vps",\
> > +        .value    = "0x40",\
> > +    },
> >
> >  #define PC_COMPAT_2_9 \
> >      HW_COMPAT_2_9 \
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 69676e1..2702485 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -4145,6 +4145,7 @@ static Property x86_cpu_properties[] = {
> >                       false),
> >      DEFINE_PROP_BOOL("vmware-cpuid-freq", X86CPU,
> vmware_cpuid_freq, true),
> >      DEFINE_PROP_BOOL("tcg-cpuid", X86CPU, expose_tcg, true),
> > +    DEFINE_PROP_INT32("x-hv-max-vps", X86CPU, hv_max_vps, -1),
> >      DEFINE_PROP_END_OF_LIST()
> >  };
> >
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index 525d35d..5c726f3 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > @@ -1282,6 +1282,8 @@ struct X86CPU {
> >      int32_t socket_id;
> >      int32_t core_id;
> >      int32_t thread_id;
> > +
> > +    int32_t hv_max_vps;
> >  };
> >
> >  static inline X86CPU *x86_env_get_cpu(CPUX86State *env)
> > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > index 6db7783..a898bef 100644
> > --- a/target/i386/kvm.c
> > +++ b/target/i386/kvm.c
> > @@ -751,7 +751,20 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >
> >          c = &cpuid_data.entries[cpuid_i++];
> >          c->function = HYPERV_CPUID_IMPLEMENT_LIMITS;
> > -        c->eax = 0x40;
> > +
> > +        /*
> > +         * From "Requirements for Implementing the Microsoft
> > +         * Hypervisor Interface":
> > +         *
> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/referenc
> e/tlfs
> > +         *
> > +         * "Starting with Windows Server 2012 and Windows 8, if
> > +         * CPUID.40000005.EAX contains a value of -1, Windows assumes
> > +         * specific limit to the number of VPs. In this case, Windows
> > +         * Server 2012 guest VMs may use more than 64 VPs, up to the
> > +         * maximum supported number of processors applicable to the
> > +         * specific Windows version being used."
> > +         */
> 
> I would place this comment above the DEFINE_PROP_INT32
> declaration, as its purpose is to explain the -1 default.
> 
Fine, do I need to send v2? Or you adjust it directly?

Thanks,
-Gonglei
> 
> > +        c->eax = cpu->hv_max_vps;
> >          c->ebx = 0x40;
> >
> >          kvm_base = KVM_CPUID_SIGNATURE_NEXT;
> > --
> > 1.8.3.1
> >
> >
> 
> --
> Eduardo