linux-kernel - RE: [PATCH 1/1] Drivers: hv: Implement the file copy service

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Date:	Thu, 9 Jan 2014 21:05:05 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	"olaf@...fle.de" <olaf@...fle.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH 1/1] Drivers: hv: Implement the file copy service



> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> Sent: Thursday, January 09, 2014 12:09 PM
> To: KY Srinivasan
> Cc: olaf@...fle.de; gregkh@...uxfoundation.org; jasowang@...hat.com; linux-
> kernel@...r.kernel.org; apw@...onical.com; devel@...uxdriverproject.org
> Subject: Re: [PATCH 1/1] Drivers: hv: Implement the file copy service
> 
> We've had this discussion before where you urge me to trust the host...

I am just implementing the protocol specification given by the host. If I cannot trust the
specified protocol, I am not sure what else can be done here. 

> 
>  Problem: This code is racy.
> Solution: The host will only send one message at a time.

The code is not racy given the protocol that is specified. While I could have 
blindly trusted the host, this driver code actually reads only one packet at a time.
When we get a transaction from the host, we do not process any more transactions until
the current transaction is fully processed. So what is the race condition here?

> 
> Now I have to audit the user space code on the host and I don't feel
> like doing that so you win.

I don't think you need to audit any code.

> 
> I wish we had a better way to do IPC.  If kdbus were ready, that might
> have worked for this, and it's a better solution because both sender and
> reciever code will be written in a less trusting way.

I am not sure how kdbus would help you here. We are talking about communicating
between the host and the guest here. 

K. Y
> 
> regards,
> dan carpenter

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