linux-kernel - Re: IOMMU keeping mapping over long period of time

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Message-ID: <CAH3drwY34arDrp=7m-_XaQ9bFwbDgw5RoWYD9_EQS5M6ySNFEw@mail.gmail.com>
Date:	Tue, 18 Oct 2011 12:09:10 -0400
From:	Jerome Glisse <j.glisse@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: IOMMU keeping mapping over long period of time

On Tue, Oct 18, 2011 at 11:56 AM, Andi Kleen <andi@...stfloor.org> wrote:
> Jerome Glisse <j.glisse@...il.com> writes:
>>
>> GPU for which we are interested have dma mask of 40bits at least, thus
>> they can work with high mem page. My main concern is when an iommu is
>> active, such amount of continuously mapped page might exhaust the iommu
>> address space. My understanding is that Intel & AMD iommu are capable of
>> growing their address space but is it somethings we can rely on ?
>
> I don't think relying on this is very wise. Better add some way to unmap
> when space is running short.
>
> -Andi
>

Maybe i should have add that the usecase involve the driver never knowing when
the GPU will make use of the mapped memory and this can happen anytime.

Cheers,
Jerome
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