Re: [PATCH 0/6] get rid of on-stack dma buffers

From: David Miller
Date: Tue Mar 22 2011 - 16:15:19 EST

From: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 22 Mar 2011 08:35:04 -0500

> The API will round up so that the correct region covers the API.
> However, if you have other structures packed into the space (as very
> often happens on stack), you get cache line interference in the CPU if
> they get accessed: The act of accessing an adjacent object pulls in
> cache above your object and destroys DMA coherence. This is the
> principle reason why DMA to stack is a bad idea.

Another major real reason we can't DMA on-stack stuff is because the
stack is mapped virtually on some platforms.

And that is the original reason the restriction was put in place.
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