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Re: [Qemu-devel] [PATCH 2/2] i386/cpu/hyperv: support over 64 vcpus for
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] i386/cpu/hyperv: support over 64 vcpus for windows guests |
Date: |
Sat, 9 Sep 2017 17:46:29 -0300 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
On Thu, Sep 07, 2017 at 01:05:33AM +0000, Gonglei (Arei) wrote:
>
>
> > -----Original Message-----
> > From: Eduardo Habkost [mailto:address@hidden
> > Sent: Tuesday, September 05, 2017 9:17 PM
> > To: Gonglei (Arei)
> > Cc: address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden;
> > Huangweidong (C)
> > Subject: Re: [PATCH 2/2] i386/cpu/hyperv: support over 64 vcpus for windows
> > guests
> >
> > On Tue, Sep 05, 2017 at 05:30:05PM +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 "hv-cpuid-limits-eax" as Paolo's suggestion, and set it
> > > to "on" before machine 2.10.
> > >
> > > 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 | 18 +++++++++++++++++-
> > > 4 files changed, 25 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > > index 8226904..db32e58 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 = "hv_cpuid_limits_eax",\
> >
> > The property name is hv-cpuid-limits-eax.
> >
> Make sense to me.
>
> > > + .value = "on",\
> > > + },\
> > >
> > > #define PC_COMPAT_2_9 \
> > > HW_COMPAT_2_9 \
> > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > index 69676e1..0d47bdd 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_BOOL("hv-cpuid-limits-eax", X86CPU,
> > hv_cpuid_limits_eax, false),
> >
> > The property name "hv-cpuid-limits-eax" doesn't say anything
> > about what it does exactly when set to true.
> >
> > What about just making it int32? e.g.:
> >
> > DEFINE_PROP_INT32("x-hv-max-vps", X86CPU, hv_max_vps, -1)
> > [...]
> > {\
> > .driver = TYPE_X86_CPU,\
> > .property = "x-hv-max-vps",\
> > .value = "0x40",\
> > },\
> > [...]
> > c->function = HYPERV_CPUID_IMPLEMENT_LIMITS;
> > c->eax = cpu->hv_max_vps;
> >
> >
> > (The "x-" prefix indicates that the property is not supposed to
> > be a stable user interface.)
> >
> I thought about this as well.
> but actually we can't assure that users set the x-hv-max-vps an invalid value
> if
> we use this method. Do we really need to expose eax directly?
We don't really need to expose eax directly and I'm not against a
boolean property, but I think an integer property with the actual
CPUID value makes the compat code simpler and the purpose of the
entry at PC_COMPAT_* more obvious.
Properties prefixed with "x-" are for internal QEMU usage or
debugging, if users want to fiddle with it, they do it at their
own risk. I don't see a problem with that.
>
> >
> > > DEFINE_PROP_END_OF_LIST()
> > > };
> > >
> > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > > index 525d35d..f8b455a 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;
> > > +
> > > + bool hv_cpuid_limits_eax;
> > > };
> > >
> > > static inline X86CPU *x86_env_get_cpu(CPUX86State *env)
> > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > > index 6db7783..cf6ef96 100644
> > > --- a/target/i386/kvm.c
> > > +++ b/target/i386/kvm.c
> > > @@ -751,7 +751,23 @@ int kvm_arch_init_vcpu(CPUState *cs)
> > >
> > > c = &cpuid_data.entries[cpuid_i++];
> > > c->function = HYPERV_CPUID_IMPLEMENT_LIMITS;
> > > - c->eax = 0x40;
> > > +
> > > + if (!cpu->hv_cpuid_limits_eax) {
> > > + /*
> > > + * 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.
> >
> > That was a direct quote from a document, so I recommend citing
> > the specific document you quoted. e.g.:
> >
> > /*
> > * 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."
> > */
> >
> >
> > > + *
> > > + * https://docs.microsoft.com/en-us/virtualization/
> > > + * hyper-v-on-windows/reference/tlfs
> >
> > IMO a long line is preferable to a broken URL.
> >
> Make sense to me.
>
> Thanks,
> -Gonglei
>
--
Eduardo