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

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Date:   Fri, 1 May 2020 13:51:06 -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 04:32:34PM -0400, Joshua Abraham wrote:
> On Fri, May 01, 2020 at 01:18:36PM -0700, Sean Christopherson wrote:
> > No, the current documentation is correct.  It's probably not as clear as
> > it could be, but it's accurate as written.  More below.
> > 
> > The ioctl() signals to the host kernel that host userspace has paused the
> > vCPU.
> > 
> > >  The host will set a flag in the pvclock structure that is checked
> > 
> > The host kernel, i.e. KVM, then takes that information and forwards it to
> > the guest kernel via the aforementioned pvclock flag.
> > 
> > The proposed change would imply the ioctl() is somehow getting routed
> > directly to the guest, which is wrong.
> 
> The rationale is that the guest is what consumes the pvclock flag, the
> host kernel does nothing interesting (from the API caller perspective) 
> besides setting up the kvmclock update. The ioctl calls kvm_set_guest_paused() 
> which even has a comment saying "[it] indicates to the guest kernel that it has 
> been stopped by the hypervisor." I think that the docs first sentence should 
> clearly reflect that the API tells the guest that it has been paused. 

I don't disagree, but simply doing s/host/guest yields a misleading
sentence and inconsistencies with the rest of the paragraph.