RE: [PATCH V2 05/18] Drivers: hv: vmbus: Consolidate all Hyper-V specific clocksource code

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Greg KH [mailto:gregkh@linuxfoundation.org]
> Sent: Thursday, January 19, 2017 10:52 AM
> To: KY Srinivasan <kys@microsoft.com>
> Cc: olaf@aepfle.de; jasowang@redhat.com; linux-kernel@vger.kernel.org;
> apw@canonical.com; devel@linuxdriverproject.org;
> leann.ogasawara@canonical.com
> Subject: Re: [PATCH V2 05/18] Drivers: hv: vmbus: Consolidate all Hyper-V
> specific clocksource code
> 
> On Thu, Jan 19, 2017 at 04:49:35PM +0000, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > Sent: Thursday, January 19, 2017 4:59 AM
> > > To: KY Srinivasan <kys@microsoft.com>
> > > Cc: linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
> > > olaf@aepfle.de; apw@canonical.com; vkuznets@redhat.com;
> > > jasowang@redhat.com; leann.ogasawara@canonical.com
> > > Subject: Re: [PATCH V2 05/18] Drivers: hv: vmbus: Consolidate all Hyper-V
> > > specific clocksource code
> > >
> > > On Wed, Jan 18, 2017 at 04:45:04PM -0700, kys@exchange.microsoft.com
> > > wrote:
> > > > From: K. Y. Srinivasan <kys@microsoft.com>
> > > >
> > > > As part of the effort to separate out architecture specific code,
> > > > consolidate all Hyper-V specific clocksource code to an architecture
> > > > specific code.
> > > >
> > > > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> > > > ---
> > > >  arch/x86/hyperv/hv_init.c       |  104
> > > +++++++++++++++++++++++++++++++++++++++
> > > >  arch/x86/include/asm/mshyperv.h |   12 +++++
> > > >  arch/x86/kernel/cpu/mshyperv.c  |   23 ---------
> > > >  drivers/hv/hv.c                 |   95 -----------------------------------
> > > >  drivers/hv/hyperv_vmbus.h       |    8 ---
> > > >  5 files changed, 116 insertions(+), 126 deletions(-)
> > > >
> > > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > > > index b5c8e04..691dfaf 100644
> > > > --- a/arch/x86/hyperv/hv_init.c
> > > > +++ b/arch/x86/hyperv/hv_init.c
> > > > @@ -24,6 +24,79 @@
> > > >  #include <linux/version.h>
> > > >  #include <linux/vmalloc.h>
> > > >  #include <linux/mm.h>
> > > > +#include <linux/clockchips.h>
> > > > +
> > > > +
> > > > +#ifdef CONFIG_X86_64
> > > > +
> > > > +static struct ms_hyperv_tsc_page *tsc_pg;
> > > > +
> > > > +static u64 read_hv_clock_tsc(struct clocksource *arg)
> > > > +{
> > > > +	u64 current_tick;
> > > > +
> > > > +	if (tsc_pg->tsc_sequence != 0) {
> > > > +		/*
> > > > +		 * Use the tsc page to compute the value.
> > > > +		 */
> > > > +
> > > > +		while (1) {
> > > > +			u64 tmp;
> > > > +			u32 sequence = tsc_pg->tsc_sequence;
> > > > +			u64 cur_tsc;
> > > > +			u64 scale = tsc_pg->tsc_scale;
> > > > +			s64 offset = tsc_pg->tsc_offset;
> > > > +
> > > > +			rdtscll(cur_tsc);
> > > > +			/* current_tick = ((cur_tsc *scale) >> 64) + offset */
> > > > +			asm("mulq %3"
> > > > +				: "=d" (current_tick), "=a" (tmp)
> > > > +				: "a" (cur_tsc), "r" (scale));
> > > > +
> > > > +			current_tick += offset;
> > > > +			if (tsc_pg->tsc_sequence == sequence)
> > > > +				return current_tick;
> > > > +
> > > > +			if (tsc_pg->tsc_sequence != 0)
> > > > +				continue;
> > > > +			/*
> > > > +			 * Fallback using MSR method.
> > > > +			 */
> > > > +			break;
> > > > +		}
> > > > +	}
> > > > +	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
> > > > +	return current_tick;
> > > > +}
> > > > +
> > > > +static struct clocksource hyperv_cs_tsc = {
> > > > +		.name		= "hyperv_clocksource_tsc_page",
> > > > +		.rating		= 400,
> > > > +		.read		= read_hv_clock_tsc,
> > > > +		.mask		= CLOCKSOURCE_MASK(64),
> > > > +		.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
> > > > +};
> > > > +#endif
> > > > +
> > > > +static u64 read_hv_clock_msr(struct clocksource *arg)
> > > > +{
> > > > +	u64 current_tick;
> > > > +	/*
> > > > +	 * Read the partition counter to get the current tick count. This count
> > > > +	 * is set to 0 when the partition is created and is incremented in
> > > > +	 * 100 nanosecond units.
> > > > +	 */
> > > > +	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
> > > > +	return current_tick;
> > > > +}
> > > > +
> > > > +static struct clocksource hyperv_cs_msr = {
> > > > +	.name		= "hyperv_clocksource_msr",
> > > > +	.rating		= 400,
> > > > +	.read		= read_hv_clock_msr,
> > > > +	.mask		= CLOCKSOURCE_MASK(64),
> > > > +	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
> > > > +};
> > > >
> > > >  static void *hypercall_pg;
> > > >  /*
> > > > @@ -31,6 +104,7 @@
> > > >   * hypervisor has been detected.
> > > >   *
> > > >   * 1. Setup the hypercall page.
> > > > + * 2. Register Hyper-V specific clocksource.
> > > >   */
> > > >  void hyperv_init(void)
> > > >  {
> > > > @@ -58,6 +132,36 @@ void hyperv_init(void)
> > > >  	hypercall_msr.enable = 1;
> > > >  	hypercall_msr.guest_physical_address =
> > > vmalloc_to_pfn(hypercall_pg);
> > > >  	wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> > > > +
> > > > +	/*
> > > > +	 * Register Hyper-V specific clocksource.
> > > > +	 */
> > > > +#ifdef CONFIG_X86_64
> > > > +	if (ms_hyperv.features &
> > > HV_X64_MSR_REFERENCE_TSC_AVAILABLE) {
> > > > +		union hv_x64_msr_hypercall_contents tsc_msr;
> > > > +
> > > > +		tsc_pg = __vmalloc(PAGE_SIZE, GFP_KERNEL,
> > > PAGE_KERNEL);
> > > > +		if (!tsc_pg)
> > > > +			clocksource_register_hz(&hyperv_cs_msr,
> > > NSEC_PER_SEC/100);
> > > > +			return;
> > >
> > > There's a reason you always test-build your patches and pay attention to
> > > the warnings!
> > >
> > > How did this pass your tests?
> > >
> > > I've stopped applying patches here.
> >
> > Greg,
> >
> > Thank you for spotting the issue; I will fix the problem and resend.
> 
> Again, I have to ask, how did this past testing?

The patches were developed on one machine and testing was done
on a different machine. While the bug was fixed on the test machine
I forgot to pick up the fix prior to posting the patches.

Regards,

K. Y