linux-kernel - RE: [PATCH v2 2/2] locking/pvqspinlock, hv: Enable PV qspinlock for Hyper-V

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Date:   Fri, 21 Sep 2018 17:02:54 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Yi Sun <yi.y.sun@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "chao.p.peng@...el.com" <chao.p.peng@...el.com>,
        "chao.gao@...el.com" <chao.gao@...el.com>,
        "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: RE: [PATCH v2 2/2] locking/pvqspinlock, hv: Enable PV qspinlock for
 Hyper-V

From: Yi Sun <yi.y.sun@...ux.intel.com> Sent: Friday, September 21, 2018 12:25 AM
> +
> +#define pr_fmt(fmt) "hv: " fmt

Other Hyper-V messages use "Hyper-V: " as the prefix, not "hv: ".  Take
a quick look at 'dmesg' output for reference.

> +
> +#include <linux/kernel_stat.h>
> +#include <linux/spinlock.h>
> +#include <linux/debugfs.h>
> +#include <linux/log2.h>
> +#include <linux/gfp.h>

Some of these #includes look like they might be leftovers from
some other code.  Please check and see whether kernel_stat.h,
debugsfs.h, log2.h, and gfp.h are actually needed.

> +static void hv_qlock_wait(u8 *byte, u8 val)
> +{
> +	unsigned long msr_val;
> +
> +	if (READ_ONCE(*byte) != val)
> +		return;
> +
> +	/*
> +	 * Read HV_X64_MSR_GUEST_IDLE MSR can trigger the guest's
> +	 * transition to the idle power state which can be exited
> +	 * by an IPI even if IF flag is disabled.
> +	 */
> +	if (ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)

I can't see a case where this test is actually needed.  hv_qlock_wait()
can only get called if the flag is set when hv_init_spinlocks() is run, and
the flag value doesn't change after it is set.

> +		rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val);
> +}

Michael