From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mukesh Rathor <mukesh.rathor@oracle.com>
Subject: Re: current not very current (vs curr_vcpu)
Date: Fri, 19 Feb 2010 11:23:49 -0800
Message-ID: <20100219112349.2cd1854a@mantra.us.oracle.com>
References: <20100218202158.6e3aeda1@mantra.us.oracle.com>
	<C7A3F862.A995%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <C7A3F862.A995%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: "Xen-devel@lists.xensource.com" <Xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

On Fri, 19 Feb 2010 08:12:18 +0000
Keir Fraser <keir.fraser@eu.citrix.com> wrote:

> On 19/02/2010 04:21, "Mukesh Rathor" <mukesh.rathor@oracle.com> wrote:
> 
> > I noticed while debugging something that current is not pointing to
> > the current vcpu upon serial interrupt. The regs->SP clearly shows
> > 64bit dom0 stack, guest_mode(regs) returns 1, but current is
> > pointing to idle vcpu. I'm not able to figure how this is possible.
> > I can come up with scenario where dom0.vcpu yields cpu to idle vcpu
> > in which case curr_vcpu will point to dom0.vcpu and current to idle
> > vcpu. But in that case guest_mode(regs) will be false, and regs.SP
> > will show hyp stack. Correct?
> > 
> > Am I correct that if guest_mode() then current should always point
> > to guest vcpu? If yes, then I will debug this further.
> 
> The behaviour you see is expected. Guest_mode() is meaningless when
> running an idle vcpu. This is because the guest regs at the bottom of
> the stack are junk for an idle vcpu (and also we do lazy state
> synchronisation, so they may be the valid active regs for the last
> scheduled non-idle vcpu).
> 
>  -- Keir
> 

Yes, but my point is it doesn't appear to be running idle vcpu as
indicated by regs->rsp and regs->rip. They both point to dom0 context.
This from printk in ns16550_interrupt().

To rephrase the question, if regs->rip and regs->rsp show guest context
in do_IRQ(), then current must always point to guest vcpu, correct?

thanks,
Mukesh