linux-kernel - Re: Regression due to d98849aff879 (dma-direct: handle DMA_ATTR_NO_KERNEL

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Message-ID: <20190806160709.GA25586@lst.de>
Date:   Tue, 6 Aug 2019 18:07:09 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Lucas Stach <l.stach@...gutronix.de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: Regression due to d98849aff879 (dma-direct: handle
 DMA_ATTR_NO_KERNEL_MAPPING in common code)

On Tue, Aug 06, 2019 at 03:59:40PM +0000, Lendacky, Thomas wrote:
> As long as two different cookie types (page pointer for encrypted DMA
> and virtual address returned from page_address() for unencrypted DMA)
> is ok. I'm just not familiar with how the cookie is used in any other
> functions, if at all.

DMA_ATTR_NO_KERNEL_MAPPING is intended for memory never used in the
kernel, either because it is just a buffer for device that are too cheap
to enough dram, or because it is a buffer for userspace to device
communication that the kernel just mediates.