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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Ram Pai <linuxram@us.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Jason Wang <jasowang@redhat.com>,
	Alexey Kardashevskiy <aik@linux.ibm.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Paul Mackerras <paulus@ozlabs.org>,
	iommu@lists.linux-foundation.org,
	linuxppc-devel@lists.ozlabs.org, Christoph Hellwig <hch@lst.de>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted
Date: Sun, 11 Aug 2019 04:44:17 -0400	[thread overview]
Message-ID: <20190811044256-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20190811064621.GB5964@ram.ibm.com>

On Sat, Aug 10, 2019 at 11:46:21PM -0700, Ram Pai wrote:
> On Sun, Aug 11, 2019 at 07:56:07AM +0200, Christoph Hellwig wrote:
> > sev_active() is gone now in linux-next, at least as a global API.
> > 
> > And once again this is entirely going in the wrong direction.  The only
> > way using the DMA API is going to work at all is if the device is ready
> > for it.  So we need a flag on the virtio device, exposed by the
> > hypervisor (or hardware for hw virtio devices) that says:  hey, I'm real,
> > don't take a shortcut.
> > 
> > And that means on power and s390 qemu will always have to set thos if
> > you want to be ready for the ultravisor and co games.  It's not like we
> > haven't been through this a few times before, have we?
> 
> 
> We have been through this so many times, but I dont think, we ever
> understood each other.   I have a fundamental question, the answer to
> which was never clear. Here it is...
> 
> If the hypervisor (hardware for hw virtio devices) does not mandate a
> DMA API, why is it illegal for the driver to request, special handling
> of its i/o buffers? Why are we associating this special handling to
> always mean, some DMA address translation? Can't there be 
> any other kind of special handling needs, that has nothing to do with
> DMA address translation?

I think the answer to that is, extend the DMA API to cover that special
need then. And that's exactly what dma_addr_is_phys_addr is trying to
do.

> 
> -- 
> Ram Pai
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  reply	other threads:[~2019-08-11  8:44 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-29 17:08 [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted Thiago Jung Bauermann
2019-01-29 17:42 ` Thiago Jung Bauermann
2019-01-29 19:02   ` Michael S. Tsirkin
2019-01-30  2:24     ` Jason Wang
2019-01-30  2:36       ` Michael S. Tsirkin
2019-01-30  3:05         ` Jason Wang
2019-01-30  3:26           ` Michael S. Tsirkin
2019-01-30  7:44         ` Christoph Hellwig
2019-02-04 18:15           ` Thiago Jung Bauermann
2019-02-04 21:38             ` Michael S. Tsirkin
2019-02-05  7:24               ` Christoph Hellwig
     [not found]                 ` <20190205072407.GA4311-jcswGhMUV9g@public.gmane.org>
2019-02-05 16:13                   ` Michael S. Tsirkin
2019-03-26 16:53           ` Michael S. Tsirkin
2019-02-04 18:14     ` Thiago Jung Bauermann
2019-02-04 20:23       ` Michael S. Tsirkin
2019-03-20 16:13         ` Thiago Jung Bauermann
2019-03-20 21:17           ` Michael S. Tsirkin
2019-03-22  0:05             ` Thiago Jung Bauermann
2019-03-23 21:01               ` Michael S. Tsirkin
2019-03-25  0:57                 ` David Gibson
2019-04-17 21:42                   ` Thiago Jung Bauermann
2019-04-17 21:42                     ` Thiago Jung Bauermann
     [not found]                 ` <20190323165456-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2019-04-17 21:42                   ` Thiago Jung Bauermann
2019-04-17 21:42                     ` Thiago Jung Bauermann
2019-04-19 23:09                     ` Michael S. Tsirkin
2019-04-19 23:09                       ` Michael S. Tsirkin
2019-04-25  1:01                       ` Thiago Jung Bauermann
2019-04-25  1:01                         ` Thiago Jung Bauermann
     [not found]                         ` <875zr228zf.fsf-wxVGo8vDogbJvNEK5ZsId7p2dZbC/Bob@public.gmane.org>
2019-04-25  1:18                           ` Michael S. Tsirkin
2019-04-25  1:18                             ` Michael S. Tsirkin
2019-04-26 23:56                             ` Thiago Jung Bauermann
2019-04-26 23:56                               ` Thiago Jung Bauermann
2019-05-20 13:08                               ` Michael S. Tsirkin
2019-05-20 13:16                     ` Michael S. Tsirkin
2019-06-04  1:13                       ` Thiago Jung Bauermann
2019-06-04  1:42                         ` Michael S. Tsirkin
2019-06-28  1:58                           ` Thiago Jung Bauermann
2019-07-01 14:17                             ` Michael S. Tsirkin
2019-07-14  5:51                               ` Thiago Jung Bauermann
2019-07-15 14:35                                 ` Michael S. Tsirkin
2019-07-15 20:29                                   ` Thiago Jung Bauermann
2019-07-15 20:36                                     ` Michael S. Tsirkin
2019-07-15 22:03                                       ` Thiago Jung Bauermann
2019-07-15 22:16                                         ` Michael S. Tsirkin
2019-07-15 23:05                                           ` Thiago Jung Bauermann
2019-07-15 23:24                                         ` Benjamin Herrenschmidt
2019-07-18  3:39                                 ` Thiago Jung Bauermann
2019-08-10 18:57 ` Michael S. Tsirkin
2019-08-10 22:07   ` Ram Pai
2019-08-11  5:56     ` Christoph Hellwig
2019-08-11  6:46       ` Ram Pai
2019-08-11  8:44         ` Michael S. Tsirkin [this message]
2019-08-12 12:13         ` Christoph Hellwig
2019-08-12 20:29           ` Ram Pai
2019-08-11  8:42       ` Michael S. Tsirkin
2019-08-11  8:55       ` Michael S. Tsirkin
2019-08-12 12:15         ` Christoph Hellwig
2019-09-06  5:07           ` Michael S. Tsirkin
2019-08-12  9:51       ` David Gibson
2019-08-13 13:26         ` Christoph Hellwig
2019-08-13 14:24           ` David Gibson
2019-08-13 15:45             ` Ram Pai
2019-08-26 17:48               ` Ram Pai
2019-08-11  8:12     ` Michael S. Tsirkin

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