linux-kernel - Re: [Pkg-xen-devel] ioatdma: Boot process hangs then reboots when using Xen + Linux 3.2

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Date:	Fri, 2 Mar 2012 12:16:47 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Nieder <jrnieder@...il.com>,
	xen-devel@...ts.xensource.com,
	pkg-xen-devel@...ts.alioth.debian.org,
	Maciej Sosnowski <maciej.sosnowski@...el.com>,
	linux-kernel@...r.kernel.org, William Dauchy <wdauchy@...il.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Dave Jiang <dave.jiang@...el.com>
Subject: Re: [Pkg-xen-devel] ioatdma: Boot process hangs then reboots when
 using Xen + Linux 3.2

On Fri, Mar 2, 2012 at 12:08 PM, Bastian Blank <waldi@...ian.org> wrote:
> On Fri, Mar 02, 2012 at 11:31:56AM -0800, Dan Williams wrote:
>> On Fri, Mar 2, 2012 at 9:57 AM, Bastian Blank <waldi@...ian.org> wrote:
>> > phys_complete (a 32 bit value) gets compared to struct
>> > dma_async_tx_descriptor.phys, which is defined as dma_addr_t, a _64_ bit
>> > value.
>> The assumption is that the driver's control structures are not in high
>> memory so all address values will only have 32-bits of valid data,
>
> Can you back that up by some kernel documentation? There is a reason why
> pci_alloc_pool uses dma_addr_t to store the address and _not_ unsigned
> long. This are physical addresses, nothing the kernel can access
> directly without a mapping.

High memory can only be accessed with kmap(), so the assumption is
that dma_alloc never gives a buffer address above 32-bits on a 32-bit
build.  Yes, if HIGHMEM64G is set dma_addr_t becomes 64-bit, but that
is only to access high memory mapped application buffers via dma_map.
I'm not aware of any documentation in this area.

I don't mind bumping up the size if xen32 is changing the above
assumptions, but I'd want confirmation that this is the failure
scenario.
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