linux-kernel - RE: [PATCH 3/3] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts

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Message-ID: <4b1cb126e6f94d26be741b7b98b58a75@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Thu, 31 Jan 2013 14:55:54 +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 3/3] X86: Handle Hyper-V vmbus interrupts as special
 hypervisor interrupts



> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@...e.com]
> Sent: Wednesday, January 30, 2013 3:59 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 3/3] X86: Handle Hyper-V vmbus interrupts as special
> hypervisor interrupts
> 
> >>> On 30.01.13 at 01:51, "K. Y. Srinivasan" <kys@...rosoft.com> wrote:
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -14,10 +14,15 @@
> >  #include <linux/time.h>
> >  #include <linux/clocksource.h>
> >  #include <linux/module.h>
> > +#include <linux/hardirq.h>
> > +#include <linux/interrupt.h>
> >  #include <asm/processor.h>
> >  #include <asm/hypervisor.h>
> >  #include <asm/hyperv.h>
> >  #include <asm/mshyperv.h>
> > +#include <asm/desc.h>
> > +#include <asm/idle.h>
> > +#include <asm/irq_regs.h>
> >
> >  struct ms_hyperv_info ms_hyperv;
> >  EXPORT_SYMBOL_GPL(ms_hyperv);
> > @@ -77,6 +82,12 @@ static void __init ms_hyperv_init_platform(void)
> >
> >  	if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
> >  		clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
> > +#if IS_ENABLED(CONFIG_HYPERV)
> > +	/*
> > +	 * Setup the IDT for hypervisor callback.
> > +	 */
> > +	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> hyperv_callback_vector);
> > +#endif
> >  }
> >
> >  const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {
> > @@ -85,3 +96,30 @@ const __refconst struct hypervisor_x86
> x86_hyper_ms_hyperv = {
> >  	.init_platform		= ms_hyperv_init_platform,
> >  };
> >  EXPORT_SYMBOL(x86_hyper_ms_hyperv);
> > +
> > +static int vmbus_irq = -1;
> > +static irq_handler_t vmbus_isr;
> > +
> > +void hv_register_vmbus_handler(int irq, irq_handler_t handler)
> > +{
> > +	vmbus_irq = irq;
> > +	vmbus_isr = handler;
> > +}
> > +EXPORT_SYMBOL_GPL(hv_register_vmbus_handler);
> > +
> > +void hyperv_vector_handler(struct pt_regs *regs)
> > +{
> > +	struct pt_regs *old_regs = set_irq_regs(regs);
> > +	struct irq_desc *desc;
> > +
> > +	irq_enter();
> > +	exit_idle();
> > +
> > +	desc = irq_to_desc(vmbus_irq);
> > +
> > +	if (desc)
> > +		generic_handle_irq_desc(vmbus_irq, desc);
> > +
> > +	irq_exit();
> > +	set_irq_regs(old_regs);
> > +}
> 
> This function appears to be dead code when !CONFIG_HYPERV,
> because ...

I will make the necessary adjustments to deal with this.

> 
> > --- a/arch/x86/kernel/entry_32.S
> > +++ b/arch/x86/kernel/entry_32.S
> > @@ -1046,11 +1046,18 @@ ENTRY(xen_failsafe_callback)
> >  	_ASM_EXTABLE(4b,9b)
> >  ENDPROC(xen_failsafe_callback)
> >
> > -BUILD_INTERRUPT3(xen_hvm_callback_vector,
> XEN_HVM_EVTCHN_CALLBACK,
> > +BUILD_INTERRUPT3(xen_hvm_callback_vector,
> HYPERVISOR_CALLBACK_VECTOR,
> >  		xen_evtchn_do_upcall)
> >
> >  #endif	/* CONFIG_XEN */
> >
> > +#if IS_ENABLED(CONFIG_HYPERV)
> > +
> > +BUILD_INTERRUPT3(hyperv_callback_vector,
> HYPERVISOR_CALLBACK_VECTOR,
> > +	hyperv_vector_handler)
> > +
> > +#endif /* CONFIG_HYPERV */
> > +
> >  #ifdef CONFIG_FUNCTION_TRACER
> >  #ifdef CONFIG_DYNAMIC_FTRACE
> >
> 
> ... the consumers here and below are conditional.
> 
> I also wonder why arch/x86/kernel/cpu/mshyperv.c is being built
> at all when !CONFIG_HYPERV (which would eliminate the need
> for the conditional the patch adds to ms_hyperv_init_platform()).

Linux is usable on Hyper-V in full emulation mode with the Hyper-V specific
clocksource plugged in. The current code permits that.

K. Y 

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