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SubjectRE: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts
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> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: Thursday, January 24, 2013 11:16 AM
> To: KY Srinivasan
> Cc: olaf@aepfle.de; bp@alien8.de; apw@canonical.com; x86@kernel.org;
> tglx@linutronix.de; devel@linuxdriverproject.org; gregkh@linuxfoundation.org;
> jasowang@redhat.com; linux-kernel@vger.kernel.org; hpa@zytor.com
> Subject: RE: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as
> special hypervisor interrupts
>
> >>> On 24.01.13 at 17:07, KY Srinivasan <kys@microsoft.com> wrote:
>
> >
> >> -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@suse.com]
> >> Sent: Thursday, January 24, 2013 3:48 AM
> >> To: KY Srinivasan
> >> Cc: olaf@aepfle.de; bp@alien8.de; apw@canonical.com; x86@kernel.org;
> >> tglx@linutronix.de; devel@linuxdriverproject.org;
> > gregkh@linuxfoundation.org;
> >> jasowang@redhat.com; linux-kernel@vger.kernel.org; hpa@zytor.com
> >> Subject: Re: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as
> >> special hypervisor interrupts
> >>
> >> >>> On 24.01.13 at 02:17, "K. Y. Srinivasan" <kys@microsoft.com> wrote:
> >> > @@ -69,6 +74,11 @@ static void __init ms_hyperv_init_platform(void)
> >> > ms_hyperv.features, ms_hyperv.hints);
> >> >
> >> > clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
> >> > +
> >> > + /*
> >> > + * Setup the IDT for hypervisor callback.
> >> > + */
> >> > + alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> >> hyperv_callback_vector);
> >>
> >> Isn't doing this unconditionally here as problematic as the call to
> >> clocksource_register_hz() turned out to be when Xen's Hyper-V
> >> shim reacts to the CPUID inquiry above?
> >
> > I was not sure what to make this conditional on at run-time. To the extent
> > that Xen emulation of Hyper-V is complete, this will be a problem. Does Xen
> > return all the "feature bits" of Hyper-V. I could discriminate on a feature
> > that
> > Xen does not plan to emulate.
>
> I've no idea what plans there might be, but that's the code
> there is currently:
>
> int cpuid_viridian_leaves(unsigned int leaf, unsigned int *eax,
> unsigned int *ebx, unsigned int *ecx,
> unsigned int *edx)
> {
> struct domain *d = current->domain;
>
> if ( !is_viridian_domain(d) )
> return 0;
>
> leaf -= 0x40000000;
> if ( leaf > 6 )
> return 0;
>
> *eax = *ebx = *ecx = *edx = 0;
> switch ( leaf )
> {
> case 0:
> *eax = 0x40000006; /* Maximum leaf */
> *ebx = 0x7263694d; /* Magic numbers */
> *ecx = 0x666F736F;
> *edx = 0x76482074;
> break;
> case 1:
> *eax = 0x31237648; /* Version number */
> break;
> case 2:
> /* Hypervisor information, but only if the guest has set its
> own version number. */
> if ( d->arch.hvm_domain.viridian.guest_os_id.raw == 0 )
> break;
> *eax = 1; /* Build number */
> *ebx = (xen_major_version() << 16) | xen_minor_version();
> *ecx = 0; /* SP */
> *edx = 0; /* Service branch and number */
> break;
> case 3:
> /* Which hypervisor MSRs are available to the guest */
> *eax = (CPUID3A_MSR_APIC_ACCESS |
> CPUID3A_MSR_HYPERCALL |
> CPUID3A_MSR_VP_INDEX);
> break;
> case 4:
> /* Recommended hypercall usage. */
> if ( (d->arch.hvm_domain.viridian.guest_os_id.raw == 0) ||
> (d->arch.hvm_domain.viridian.guest_os_id.fields.os < 4) )
> break;
> *eax = (CPUID4A_MSR_BASED_APIC |
> CPUID4A_RELAX_TIMER_INT);
> *ebx = 2047; /* long spin count */
> break;
> }
>
> return 1;
> }
>
> Question is - considering you stated that this is supported
> starting in Win8, doesn't Hyper-V itself announce that
> capability in some explicit way?

Thanks Jan. Unfortunately I don't think tis interrupt delivery model is
specified via a "feature" bit (I will check with the Windows guys). Perhaps, we
can have a Hyper-V specific compilation switch to address the Xen emulation issue.

Regards,

K. Y
>
> Jan
>
>




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