From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad@darnok.org>
Subject: Re: Buffers not reachable by PCI
Date: Tue, 13 Dec 2011 18:28:00 -0500
Message-ID: <20111213232759.GA8702@konrad-lan>
References: <3E243B26F475504B9BB0BCC9728B0DA629E16E01@USILMS110A.ca.com>
	<20111209203010.GA14412@andromeda.dapyr.net>
	<3E243B26F475504B9BB0BCC9728B0DA629E17AEA@USILMS110A.ca.com>
	<20111213001912.GA2730@konrad-lan>
	<3E243B26F475504B9BB0BCC9728B0DA629E184FA@USILMS110A.ca.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
Content-Disposition: inline
In-Reply-To: <3E243B26F475504B9BB0BCC9728B0DA629E184FA@USILMS110A.ca.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/options/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: "Taylor, Neal E" <Neal.Taylor@ca.com>
Cc: xen-devel <xen-devel@lists.xensource.com>, "Kalev,
	Leonid" <Leonid.Kalev@ca.com>, "Dave, Tushar N" <tushar.n.dave@intel.com>
List-Id: xen-devel@lists.xenproject.org

On Tue, Dec 13, 2011 at 10:17:50PM +0000, Taylor, Neal E wrote:
> 
> Is it the translation that's in error?
> 
> Modeled after the translation in xen_swiotlb_dma_supported that's used for the problematic comparison, I added "the same" translation to swiotlb_print. I don't understand the results as dend - dstart is vastly larger that pend - pstart.

You might want to instrument the xen_swiotlb_fixup code to get an idea.

But basically there are "chunks" of 2MB (I think) of contingous memory
that is swizzled in to the memory that starts at io_tlb_start. But
all of that memory SHOULD be under the 4GB limit (set by max_dma_bits).

Sadly in your case one of those "chunks" ends up being past the 4GB
limit - which should never happen. Or if it did happen it would print
out "Failed to get contiguous memory for DMA from.."

But you don't get any of that.


To get a good idea of this, you could do something like this

unsigned long mfn, next_mfn;

mfn= PFN_DOWN(phys_to_machine(XPADDR(pstart)).maddr);

for (i = pstart; i < pend;) {
	next_mfn = PFN_DOWN(phys_to_machine(XPADDR(i)).maddr);
	if (next_mfn == mfn+1) {
		mfn++;
	} else {
		printk(KERN_INFO "MFN 0x%lx->0x%lx\n", mfn, next_mfn);
		mfn = next_mfn;
	}
	i+=PAGE_SIZE;
}

which should print you those "chunks", if my logic here is right.


Can you send me your 'xl info' (or 'xl dmesg'), please?

I tried to reproduce this with a 3.0.4 kernel on a 8GB and I couldn't
reproduce this. Hm, will look in your .config in case there is something
funky there.