Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance

From: Grant Grundler
Date: Thu Aug 08 2013 - 14:28:50 EST


On Thu, Aug 8, 2013 at 6:54 AM, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote:
>> + BUG_ON(lv1ent_section(sent));
> Is this condition really a critical one, to the point that the system
> should not continue execution?
>> if (lv1ent_page(sent)) {
>> - if (*pgcnt != NUM_LV2ENTRIES)
>> - return -EADDRINUSE;
>> -
>> + BUG_ON(*pgcnt != NUM_LV2ENTRIES);
> Ditto.

I can't speak to the previous BUG_ON(). I believe the EADDRESSINUSE
failures could be either WARN_ON or BUG_ON. This condition is
clearly a bug in the generic IOMMU allocator and I think that's why
KyongHo Cho used BUG_ON.

Handing out duplicate addresses will generally lead to some sort of
data corruption or other fault depending on how robust the underlying
device drivers are written. So my preference is a BUG_ON to
immediately flag this condition instead of hoping a device driver will
correctly handling the dma mapping failure (Some do, most currently

WARN_ON() + return -EADDRESSINUSE would be a good alternative.

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