Re: [PATCH v2 1/4] x86/mm: Export force_dma_unencrypted

From: Thomas HellstrÃm (VMware)
Date: Tue Sep 03 2019 - 10:33:02 EST

Hi, Christoph,

On 9/3/19 3:46 PM, Christoph Hellwig wrote:
On Tue, Sep 03, 2019 at 03:15:01PM +0200, Thomas HellstrÃm (VMware) wrote:
From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>

The force_dma_unencrypted symbol is needed by TTM to set up the correct
page protection when memory encryption is active. Export it.
NAK. This is a helper for the core DMA code and drivers have no
business looking at it.

Is this a layer violation concern, that is, would you be ok with a similar helper for TTM, or is it that you want to force the graphics drivers into adhering strictly to the DMA api, even when it from an engineering perspective makes no sense?

If it's the latter, then I would like to reiterate that it would be better that we work to come up with a long term plan to add what's missing to the DMA api to help graphics drivers use coherent memory?