From: "Michael S. Tsirkin" <mst@redhat.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Gibson <david@gibson.dropbear.id.au>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
aik@ozlabs.ru, robh@kernel.org, joe@perches.com,
elfring@users.sourceforge.net, jasowang@redhat.com,
mpe@ellerman.id.au, hch@infradead.org
Subject: Re: [RFC V2] virtio: Add platform specific DMA API translation for virito devices
Date: Mon, 4 Jun 2018 15:50:46 +0300 [thread overview]
Message-ID: <20180604154355-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <d5df613d6347fe2f9bb6ea65bc6f6be05650ca6f.camel@kernel.crashing.org>
On Mon, Jun 04, 2018 at 07:48:54PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2018-06-04 at 18:57 +1000, David Gibson wrote:
> >
> > > - First qemu doesn't know that the guest will switch to "secure mode"
> > > in advance. There is no difference between a normal and a secure
> > > partition until the partition does the magic UV call to "enter secure
> > > mode" and qemu doesn't see any of it. So who can set the flag here ?
> >
> > This seems weird to me. As a rule HV calls should go through qemu -
> > or be allowed to go directly to KVM *by* qemu.
>
> It's not an HV call, it's a UV call, qemu won't see it, qemu isn't
> trusted. Now the UV *will* reflect that to the HV via some synthetized
> HV calls, and we *could* have those do a pass by qemu, however, so far,
> our entire design doesn't rely on *any* qemu knowledge whatsoever and
> it would be sad to add it just for that purpose.
It's a temporary work-around. I think that the long-term fix is to
support per-device quirks and have the DMA API DTRT for virtio.
> Additionally, this is rather orthogonal, see my other email, the
> problem we are trying to solve is *not* a qemu problem and it doesn't
> make sense to leak that into qemu.
>
> > We generally reserve
> > the latter for hot path things. Since this isn't a hot path, having
> > the call handled directly by the kernel seems wrong.
> >
> > Unless a "UV call" is something different I don't know about.
>
> Yes, a UV call goes to the Ultravisor, not the Hypervisor. The
> Hypervisor isn't trusted.
>
> > > - Second, when using VIRTIO_F_IOMMU_PLATFORM, we also make qemu (or
> > > vhost) go through the emulated MMIO for every access to the guest,
> > > which adds additional overhead.
> >
> Ben.
next prev parent reply other threads:[~2018-06-04 12:50 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-22 6:33 [RFC V2] virtio: Add platform specific DMA API translation for virito devices Anshuman Khandual
2018-05-23 18:50 ` Michael S. Tsirkin
2018-05-23 22:27 ` Benjamin Herrenschmidt
2018-05-24 7:17 ` Christoph Hellwig
2018-05-25 17:45 ` Michael S. Tsirkin
2018-05-28 23:48 ` Benjamin Herrenschmidt
2018-05-28 23:56 ` Benjamin Herrenschmidt
2018-05-29 14:03 ` Christoph Hellwig
2018-05-29 22:13 ` Benjamin Herrenschmidt
2018-06-04 8:57 ` David Gibson
2018-06-04 9:48 ` Benjamin Herrenschmidt
2018-06-04 12:50 ` Michael S. Tsirkin [this message]
2018-06-05 1:52 ` David Gibson
2018-06-04 12:43 ` Michael S. Tsirkin
2018-06-04 12:55 ` Christoph Hellwig
2018-06-04 13:14 ` Benjamin Herrenschmidt
2018-06-04 16:34 ` Michael S. Tsirkin
2018-06-04 13:11 ` Benjamin Herrenschmidt
2018-06-04 16:21 ` Michael S. Tsirkin
2018-06-04 23:26 ` Benjamin Herrenschmidt
2018-06-05 1:25 ` Michael S. Tsirkin
2018-06-05 4:52 ` Christoph Hellwig
2018-05-24 7:21 ` Ram Pai
2018-05-31 3:39 ` Anshuman Khandual
2018-05-31 17:43 ` Michael S. Tsirkin
2018-06-07 5:23 ` Christoph Hellwig
2018-06-07 16:28 ` Michael S. Tsirkin
2018-06-08 6:36 ` Christoph Hellwig
2018-06-13 13:49 ` Michael S. Tsirkin
2018-06-11 2:39 ` Ram Pai
2018-06-11 3:28 ` Michael S. Tsirkin
2018-06-11 3:34 ` Benjamin Herrenschmidt
2018-06-13 14:23 ` Michael S. Tsirkin
2018-06-11 3:29 ` Benjamin Herrenschmidt
2018-06-13 7:41 ` Christoph Hellwig
2018-06-13 12:25 ` Benjamin Herrenschmidt
2018-06-13 13:11 ` Benjamin Herrenschmidt
2018-06-15 9:16 ` Christoph Hellwig
2018-06-16 1:07 ` Benjamin Herrenschmidt
2018-06-13 13:59 ` Michael S. Tsirkin
2018-06-13 14:03 ` Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180604154355-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=aik@ozlabs.ru \
--cc=benh@kernel.crashing.org \
--cc=david@gibson.dropbear.id.au \
--cc=elfring@users.sourceforge.net \
--cc=hch@infradead.org \
--cc=jasowang@redhat.com \
--cc=joe@perches.com \
--cc=khandual@linux.vnet.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=robh@kernel.org \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).