From: Halil Pasic <pasic@linux.ibm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Tom Lendacky <thomas.lendacky@amd.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>,
"Kalra, Ashish" <Ashish.Kalra@amd.com>
Subject: Re: [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails
Date: Fri, 29 Nov 2019 15:09:41 +0100 [thread overview]
Message-ID: <20191129150941.34cab07a.pasic@linux.ibm.com> (raw)
In-Reply-To: <20191126184527.GA10481@lst.de>
On Tue, 26 Nov 2019 19:45:27 +0100
Christoph Hellwig <hch@lst.de> wrote:
> On Sat, Nov 23, 2019 at 09:39:08AM -0600, Tom Lendacky wrote:
> > Ideally, having a pool of shared pages for DMA, outside of standard
> > SWIOTLB, might be a good thing. On x86, SWIOTLB really seems geared
> > towards devices that don't support 64-bit DMA. If a device supports 64-bit
> > DMA then it can use shared pages that reside anywhere to perform the DMA
> > and bounce buffering. I wonder if the SWIOTLB support can be enhanced to
> > support something like this, using today's low SWIOTLB buffers if the DMA
> > mask necessitates it, otherwise using a dynamically sized pool of shared
> > pages that can live anywhere.
>
> I think that can be done relatively easily. I've actually been thinking
> of multiple pool support for a whіle to replace the bounce buffering
> in the block layer for ISA devices (24-bit addressing).
>
> I've also been looking into a dma_alloc_pages interface to help people
> just allocate pages that are always dma addressable, but don't need
> a coherent allocation. My last version I shared is here:
>
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma_alloc_pages
>
> But it turns out this still doesn't work with SEV as we'll always
> bounce. And I've been kinda lost on figuring out a way how to
> allocate unencrypted pages that we we can feed into the normal
> dma_map_page & co interfaces due to the magic encryption bit in
> the address. I guess we could have a fallback path in the mapping
> path and just unconditionally clear that bit in the dma_to_phys
> path.
Thanks Christoph! Thanks Tom! I will do some looking and thinking and
report back.
Regards,
Halil
prev parent reply other threads:[~2019-11-29 14:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-14 12:46 [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails Halil Pasic
2019-11-19 11:10 ` Halil Pasic
2019-11-19 13:04 ` Michael S. Tsirkin
2019-11-22 13:08 ` Halil Pasic
2019-11-23 15:39 ` Tom Lendacky
2019-11-26 18:45 ` Christoph Hellwig
2019-11-28 0:42 ` Ashish Kalra
2019-11-28 7:05 ` Christoph Hellwig
2019-11-29 1:57 ` Ashish Kalra
2019-11-29 14:09 ` Halil Pasic [this message]
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