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SubjectRE: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts
From
Date
I also have to point out the obvious problem with Xen masquerading as HyperV without implementing the same feature set...

KY Srinivasan <kys@microsoft.com> wrote:

>
>
>> -----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
>>
>>

--
Sent from my mobile phone. Please excuse brevity and lack of formatting.


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