Re: [openib-general] [PATCH 11 of 20] ipath - core driver, part 4 of 4

Roland Dreier
2005-12-29T02:19:55Z

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.