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

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Date:   Thu, 19 Jan 2017 11:58:57 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     kys@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        olaf@...fle.de, apw@...onical.com, vkuznets@...hat.com,
        jasowang@...hat.com, leann.ogasawara@...onical.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@...hange.microsoft.com wrote:
> From: K. Y. Srinivasan <kys@...rosoft.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@...rosoft.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 k-h