From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:45226)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1VbqWD-0004JD-P3
	for qemu-devel@nongnu.org; Thu, 31 Oct 2013 07:34:34 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1VbqW8-0006ZF-Sz
	for qemu-devel@nongnu.org; Thu, 31 Oct 2013 07:34:29 -0400
Received: from mx1.redhat.com ([209.132.183.28]:31490)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1VbqW8-0006ZA-JH
	for qemu-devel@nongnu.org; Thu, 31 Oct 2013 07:34:24 -0400
Date: Thu, 31 Oct 2013 13:37:14 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20131031113714.GB8976@redhat.com>
References: <20131028190151.GA1994@redhat.com>
 <52723FBC.1010803@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <52723FBC.1010803@redhat.com>
Subject: Re: [Qemu-devel] [PATCH repost] ahci: fix win7 hang on boot
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, agraf@suse.de, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>

On Thu, Oct 31, 2013 at 12:32:12PM +0100, Paolo Bonzini wrote:
> Il 28/10/2013 20:01, Michael S. Tsirkin ha scritto:
> > From: Alexander Graf <agraf@suse.de>
> > 
> > When AHCI executes an asynchronous IDE command, it checked DRDY without
> > checking either DRQ or BSY.  This sometimes caused interrupt to be sent
> > before command is actually completed.
> > 
> > This resulted in a race condition: if guest then managed to access the
> > device before command has completed, it would hang waiting for an
> > interrupt.
> > This was observed with windows 7 guests.
> > 
> > To fix, check for DRQ or BSY in additiona to DRDY, if set,
> > the command is asynchronous so delay the interrupt until
> > asynchronous done callback is invoked.
> > 
> > Reported-by: Michael S. Tsirkin <mst@redhat.com>
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > Tested-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > ---
> >  hw/ide/ahci.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> > index a8be62c..fbea9e8 100644
> > --- a/hw/ide/ahci.c
> > +++ b/hw/ide/ahci.c
> > @@ -961,7 +961,8 @@ static int handle_cmd(AHCIState *s, int port, int slot)
> >          /* We're ready to process the command in FIS byte 2. */
> >          ide_exec_cmd(&s->dev[port].port, cmd_fis[2]);
> >  
> > -        if (s->dev[port].port.ifs[0].status & READY_STAT) {
> > +        if ((s->dev[port].port.ifs[0].status & (READY_STAT|DRQ_STAT|BUSY_STAT)) ==
> > +            READY_STAT) {
> >              ahci_write_fis_d2h(&s->dev[port], cmd_fis);
> >          }
> >      }
> > 
> 
> While the patch fixes the symptom, I think it is only a bandaid.
> 
> There is no reason why the async_cmd_done should be restricted to
> asynchronous commands.  If synchronous commands are made to go through
> the async_cmd_done callback, you'll automatically get the D2H FIS
> written for all commands.

I suggested this to Kevin offline but he prefers it like this.

> It's good for 1.7, but let's revisit it for 1.8.
> 
> Paolo

Fine with me.