linux-kernel - Re: [PATCH 3/4 V10] Add ioctl for KVMCLOCK_GUEST

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Message-ID: <4F26CF3D.4070001@redhat.com>
Date:	Mon, 30 Jan 2012 19:11:25 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
CC:	Eric B Munson <emunson@...bm.net>, mingo@...hat.com, hpa@...or.com,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com, mtosatti@...hat.com,
	jeremy.fitzhardinge@...rix.com, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4 V10] Add ioctl for KVMCLOCK_GUEST_STOPPED

On 01/30/2012 06:18 PM, Jan Kiszka wrote:
> > 
> > This looks racy.  The vcpu can remove its kvmclock concurrently with
> > this access, and src will be NULL.
>
> There is no race here (src is member of the vcpu), but arch.time might
> have become invalid. KVM_REQ_CLOCK_UPDATE instead of mark_page_dirty
> would indeed be the way to go. Trivial solution, I would say.
>
> However, the concept of "guest stopped" has VM, not VCPU scope. 

We're not stopping the guest here, just setting a flag in kvmclock,
which certainly is a per-vcpu thing.

> That
> makes the call more appropriate as a VM ioctl. If that thing should
> really become per-vcpu, at least call it KVMCLOCK_VCPU_STOPPED.
>

All current ioctls start with KVM_. Maybe KVM_KVMCLOCK_CTRL?

-- 
error compiling committee.c: too many arguments to function

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