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Date:   Thu, 28 Nov 2019 08:05:38 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ashish Kalra <ashish.kalra@amd.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Halil Pasic <pasic@linux.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Cornelia Huck <cohuck@redhat.com>,
        linux-s390@vger.kernel.org, Michael Mueller <mimu@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Ram Pai <linuxram@us.ibm.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails
Message-ID: <20191128070538.GB20274@lst.de>
References: <20191114124646.74790-1-pasic@linux.ibm.com> <20191119121022.03aed69a.pasic@linux.ibm.com> <20191119080420-mutt-send-email-mst@kernel.org> <20191122140827.0ead345c.pasic@linux.ibm.com> <1ec7c229-6c4f-9351-efda-ed2df20f95f6@amd.com> <20191126184527.GA10481@lst.de> <20191128004225.GA11539@ashkalra_ubuntu_server>
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On Thu, Nov 28, 2019 at 12:42:25AM +0000, Ashish Kalra wrote:
> Why can't we leverage CMA instead of SWIOTLB for DMA when SEV is
> enabled, CMA is well integerated with the DMA subsystem and handles
> encrypted pages when force_dma_unencrypted() returns TRUE. 
> 
> Though, CMA might face the same issues as SWIOTLB bounce buffers, it's
> size is similarly setup statically as SWIOTLB does or can be set as a 
> percentage of the available system memory.

How is CMA integrated with SEV?  CMA just gives a contiguous chunk
of memory, which still needs to be remapped as unencrypted before
returning it to the user.