linux-kernel - Re: [PATCH] docs: kvm: Fix KVM_KVMCLOCK

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Message-ID: <20200501213803.GF4760@linux.intel.com>
Date:   Fri, 1 May 2020 14:38:03 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Joshua Abraham <j.abraham1776@...il.com>
Cc:     pbonzini@...hat.com, corbet@....net, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] docs: kvm: Fix KVM_KVMCLOCK_CTRL API doc

On Fri, May 01, 2020 at 05:10:40PM -0400, Joshua Abraham wrote:
> On Fri, May 01, 2020 at 01:51:06PM -0700, Sean Christopherson wrote:
> > I don't disagree, but simply doing s/host/guest yields a misleading
> > sentence and inconsistencies with the rest of the paragraph.
> 
> I see your point. Would this wording be clearer:
> 
> "This ioctl sets a flag accessible to the guest indicating that it has been
> paused from the host userspace.

Ya.  Minor nit, probably worth clarifying that 'it' refers to the vCPU, e.g.

  This ioctl sets a flag accessible to the guest indicating that the specified
  vCPU has been paused by the host userspace.

> 
> The host will set a flag in the pvclock structure that is checked
> from the soft lockup watchdog.  The flag is part of the pvclock structure that
> is shared between guest and host, specifically the second bit of the flags
> field of the pvclock_vcpu_time_info structure.  It will be set exclusively by
> the host and read/cleared exclusively by the guest.  The guest operation of
> checking and clearing the flag must be an atomic operation so
> load-link/store-conditional, or equivalent must be used.  There are two cases
> where the guest will clear the flag: when the soft lockup watchdog timer resets
> itself or when a soft lockup is detected.  This ioctl can be called any time
> after pausing the vcpu, but before it is resumed."