To: "Bryan O'Sullivan" <bos@pathscale.com>
Cc: linux-kernel@vger.kernel.org, openib-general@openib.org
Subject: Re: [openib-general] [PATCH 11 of 20] ipath - core driver, part 4
 of 4
References: <e8af3873b0d910e0c623.1135816290@eng-12.pathscale.com>
From: Roland Dreier <rdreier@cisco.com>
Date: Wed, 28 Dec 2005 18:19:49 -0800
In-Reply-To: <e8af3873b0d910e0c623.1135816290@eng-12.pathscale.com> (Bryan
 O'Sullivan's message of "Wed, 28 Dec 2005 16:31:30 -0800")
Message-ID: <ada1wzwbq62.fsf@cisco.com>
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I didn't notice this before:

 > + * This is volatile as it's the target of a DMA from the chip.
 > + */
 > +
 > +static volatile uint64_t ipath_port0_rcvhdrtail[512]
 > +    __attribute__ ((aligned(4096)));

 ... and then much later ...

 > +	/*
 > +	 * kernel modules loaded into vmalloc'ed memory,
 > +	 * verify that when we assume that, map to phys, and back to virt,
 > +	 * that we get the right contents, so we did the mapping right.
 > +	 */
 > +	vpage = vmalloc_to_page((void *)ipath_port0_rcvhdrtail);
 > +	if (vpage == NOPAGE_SIGBUS || vpage == NOPAGE_OOM) {
 > +		_IPATH_UNIT_ERROR(t, "vmalloc_to_page for rcvhdrtail fails!\n");
 > +		ret = -ENOMEM;
 > +		goto done;
 > +	}

This seems very wrong to me: there's no guarantee that a module will
be loaded into memory that can be used as a DMA target.  For example,
on a non-cache-coherent architecture, I think this memory must be
accessed through a non-cached mapping.

I think the correct solution is to allocate a buffer for each device
with pci_alloc_consistent() (or maybe dma_alloc_coherent()).

(As a general comment, I'm still unhappy about how your driver has a
static, fixed-size table of devices rather than allocating per-device
data structures dynamically)

 - R.
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