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

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Message-ID: <CABE8wwtqg5eOqW19EBX+bhq2Gz6O8V6JHVgEB+zeBWpr1D92tw@mail.gmail.com>
Date:	Fri, 2 Mar 2012 13:17:07 -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 12:56 PM, Bastian Blank <waldi@...ian.org> wrote:
> On Fri, Mar 02, 2012 at 12:16:47PM -0800, Dan Williams wrote:
>> 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.
>
> All memory needs to be mapped.  Linux just have a default mapping of 1GiB
> of the memory handy. However this is irrelevant for the physical DMA
> addresses we talk about.

I'm not sure you understand how himem works or we're talking past each other.
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