linux-kernel - RE: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts

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Message-ID: <f6cbfec9c014433fa54af61d8f436ebb@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Thu, 24 Jan 2013 18:48:31 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	"olaf@...fle.de" <olaf@...fle.de>, "bp@...en8.de" <bp@...en8.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: RE: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as
 special hypervisor interrupts



> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@...e.com]
> Sent: Thursday, January 24, 2013 11:16 AM
> To: KY Srinivasan
> Cc: olaf@...fle.de; bp@...en8.de; apw@...onical.com; x86@...nel.org;
> tglx@...utronix.de; devel@...uxdriverproject.org; gregkh@...uxfoundation.org;
> jasowang@...hat.com; linux-kernel@...r.kernel.org; hpa@...or.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@...rosoft.com> wrote:
> 
> >
> >> -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@...e.com]
> >> Sent: Thursday, January 24, 2013 3:48 AM
> >> To: KY Srinivasan
> >> Cc: olaf@...fle.de; bp@...en8.de; apw@...onical.com; x86@...nel.org;
> >> tglx@...utronix.de; devel@...uxdriverproject.org;
> > gregkh@...uxfoundation.org;
> >> jasowang@...hat.com; linux-kernel@...r.kernel.org; hpa@...or.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@...rosoft.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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