linux-kernel - RE: [PATCH 5/5] Drivers: hv: vmbus: Implement a clocksource based on the TSC page

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Message-ID: <BY2PR0301MB1654FA5967C5A3630A83F5C2A0850@BY2PR0301MB1654.namprd03.prod.outlook.com>
Date:	Mon, 20 Jul 2015 18:50:52 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Dexuan Cui <decui@...rosoft.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH 5/5] Drivers: hv: vmbus: Implement a clocksource based on
 the TSC page



> -----Original Message-----
> From: Dexuan Cui
> Sent: Monday, July 20, 2015 5:14 AM
> To: KY Srinivasan; gregkh@...uxfoundation.org; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> apw@...onical.com; vkuznets@...hat.com; jasowang@...hat.com
> Subject: RE: [PATCH 5/5] Drivers: hv: vmbus: Implement a clocksource based
> on the TSC page
> 
> > From: devel [mailto:driverdev-devel-bounces...linuxdriverproject.org] On
> Behalf
> > Of K. Y. Srinivasan
> > Sent: Monday, July 20, 2015 11:37
> >
> > The current Hyper-V clock source is based on the per-partition reference
> counter
> > and this counter is being accessed via s synthetic MSR -
> > HV_X64_MSR_TIME_REF_COUNT.
> > Hyper-V has a more efficient way of computing the per-partition reference
> > counter value that does not involve reading a synthetic MSR. We
> implement
> > a time source based on this mechanism.
> > ...
> > diff --git a/arch/x86/include/uapi/asm/hyperv.h
> > @@ -183,6 +233,22 @@ int hv_init(void)
> >
> >  	hv_context.hypercall_page = virtaddr;
> >
> > +#ifdef CONFIG_X86_64
> > +	if (ms_hyperv.features &
> HV_X64_MSR_REFERENCE_TSC_AVAILABLE) {
> > +		va_tsc = __vmalloc(PAGE_SIZE, GFP_KERNEL,
> PAGE_KERNEL);
> > +		if (!va_tsc)
> > +			goto cleanup;
> > +		hv_context.tsc_page = va_tsc;
> > +
> > +		rdmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
> > +
> > +		tsc_msr.enable = 1;
> > +		tsc_msr.guest_physical_address = vmalloc_to_pfn(va_tsc);
> > +
> > +		wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
> > +		clocksource_register_hz(&hyperv_cs_tsc,
> NSEC_PER_SEC/100);
> > +	}
> > +#endif
> 
> Should we disable the mechanism and vfree() the page in hv_cleanup() for
> kexec/kdump?

Thanks Dexuan. I will update the patch and resend.

Regards,

K. Y
> 
> -- Dexuan
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