From: Christoph Hellwig <hch@infradead.org> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: Christoph Hellwig <hch@infradead.org>, Will Deacon <will.deacon@arm.com>, 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, david@gibson.dropbear.id.au, jasowang@redhat.com, benh@kernel.crashing.org, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Date: Tue, 31 Jul 2018 10:30:52 -0700 [thread overview] Message-ID: <20180731173052.GA17153@infradead.org> (raw) In-Reply-To: <20180730155633-mutt-send-email-mst@kernel.org> On Mon, Jul 30, 2018 at 04:26:32PM +0300, Michael S. Tsirkin wrote: > Real hardware would reuse parts of the interface but by necessity it > needs to behave slightly differently on some platforms. However for > some platforms (such as x86) a PV virtio driver will by luck work with a > PCI device backend without changes. As these platforms and drivers are > widely deployed, some people will deploy hardware like that. Should be > a non issue as by definition it's transparent to guests. On some x86. As soon as you have an iommu or strange PCI root ports things are going to start breaking apart. > > And that very much excludes arch-specific (or > > Xen-specific) overrides. > > We already committed to a xen specific hack but generally I prefer > devices that describe how they work instead of platforms magically > guessing, yes. For legacy reasons I guess we'll have to keep it, but we really need to avoid adding more junk than this. > However the question people raise is that DMA API is already full of > arch-specific tricks the likes of which are outlined in your post linked > above. How is this one much worse? None of these warts is visible to the driver, they are all handled in the architecture (possibly on a per-bus basis). So for virtio we really need to decide if it has one set of behavior as specified in the virtio spec, or if it behaves exactly as if it was on a PCI bus, or in fact probably both as you lined up. But no magic arch specific behavior inbetween.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, benh@kernel.crashing.org, Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org, linuxram@us.ibm.com, virtualization@lists.linux-foundation.org, Christoph Hellwig <hch@infradead.org>, paulus@samba.org, marc.zyngier@arm.com, mpe@ellerman.id.au, joe@perches.com, robin.murphy@arm.com, david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com, Anshuman Khandual <khandual@linux.vnet.ibm.com> Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Date: Tue, 31 Jul 2018 10:30:52 -0700 [thread overview] Message-ID: <20180731173052.GA17153@infradead.org> (raw) In-Reply-To: <20180730155633-mutt-send-email-mst@kernel.org> On Mon, Jul 30, 2018 at 04:26:32PM +0300, Michael S. Tsirkin wrote: > Real hardware would reuse parts of the interface but by necessity it > needs to behave slightly differently on some platforms. However for > some platforms (such as x86) a PV virtio driver will by luck work with a > PCI device backend without changes. As these platforms and drivers are > widely deployed, some people will deploy hardware like that. Should be > a non issue as by definition it's transparent to guests. On some x86. As soon as you have an iommu or strange PCI root ports things are going to start breaking apart. > > And that very much excludes arch-specific (or > > Xen-specific) overrides. > > We already committed to a xen specific hack but generally I prefer > devices that describe how they work instead of platforms magically > guessing, yes. For legacy reasons I guess we'll have to keep it, but we really need to avoid adding more junk than this. > However the question people raise is that DMA API is already full of > arch-specific tricks the likes of which are outlined in your post linked > above. How is this one much worse? None of these warts is visible to the driver, they are all handled in the architecture (possibly on a per-bus basis). So for virtio we really need to decide if it has one set of behavior as specified in the virtio spec, or if it behaves exactly as if it was on a PCI bus, or in fact probably both as you lined up. But no magic arch specific behavior inbetween.
next prev parent reply other threads:[~2018-07-31 17:31 UTC|newest] Thread overview: 240+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-07-20 3:59 [RFC 0/4] Virtio uses DMA API for all devices Anshuman Khandual 2018-07-20 3:59 ` [RFC 1/4] virtio: Define virtio_direct_dma_ops structure Anshuman Khandual 2018-07-20 3:59 ` Anshuman Khandual 2018-07-30 9:24 ` Christoph Hellwig 2018-07-30 9:24 ` Christoph Hellwig 2018-07-31 4:01 ` Anshuman Khandual 2018-07-31 4:01 ` Anshuman Khandual 2018-07-20 3:59 ` [RFC 2/4] virtio: Override device's DMA OPS with virtio_direct_dma_ops selectively Anshuman Khandual 2018-07-20 3:59 ` Anshuman Khandual 2018-07-28 8:56 ` Anshuman Khandual 2018-07-28 8:56 ` Anshuman Khandual 2018-07-28 21:16 ` Michael S. Tsirkin 2018-07-30 4:15 ` Anshuman Khandual 2018-07-30 4:15 ` Anshuman Khandual 2018-07-30 9:30 ` Christoph Hellwig 2018-07-31 6:39 ` Anshuman Khandual 2018-07-31 6:39 ` Anshuman Khandual 2018-07-30 9:30 ` Christoph Hellwig 2018-07-28 21:16 ` Michael S. Tsirkin 2018-07-30 9:25 ` Christoph Hellwig 2018-07-31 7:00 ` Anshuman Khandual 2018-07-31 7:00 ` Anshuman Khandual 2018-07-30 9:25 ` Christoph Hellwig 2018-07-20 3:59 ` [RFC 3/4] virtio: Force virtio core to use DMA API callbacks for all virtio devices Anshuman Khandual 2018-07-20 3:59 ` Anshuman Khandual 2018-07-20 3:59 ` [RFC 4/4] virtio: Add platform specific DMA API translation for virito devices Anshuman Khandual 2018-07-20 13:15 ` Michael S. Tsirkin 2018-07-20 13:15 ` Michael S. Tsirkin 2018-07-23 2:16 ` Anshuman Khandual 2018-07-23 2:16 ` Anshuman Khandual 2018-07-25 4:30 ` Anshuman Khandual 2018-07-25 4:30 ` Anshuman Khandual 2018-07-25 13:31 ` Michael S. Tsirkin 2018-07-25 13:31 ` Michael S. Tsirkin 2018-07-20 3:59 ` Anshuman Khandual 2018-07-20 13:16 ` [RFC 0/4] Virtio uses DMA API for all devices Michael S. Tsirkin 2018-07-20 13:16 ` Michael S. Tsirkin 2018-07-23 6:28 ` Anshuman Khandual 2018-07-23 9:08 ` Michael S. Tsirkin 2018-07-23 9:08 ` Michael S. Tsirkin 2018-07-25 3:26 ` Anshuman Khandual 2018-07-27 11:31 ` Michael S. Tsirkin 2018-07-27 11:31 ` Michael S. Tsirkin 2018-07-28 8:37 ` Anshuman Khandual 2018-07-28 8:37 ` Anshuman Khandual 2018-07-25 3:26 ` Anshuman Khandual 2018-07-23 6:28 ` Anshuman Khandual 2018-07-27 9:58 ` Will Deacon 2018-07-27 9:58 ` Will Deacon 2018-07-27 9:58 ` Will Deacon 2018-07-27 10:58 ` Anshuman Khandual 2018-07-27 10:58 ` Anshuman Khandual 2018-07-30 9:34 ` Christoph Hellwig 2018-07-30 9:34 ` Christoph Hellwig 2018-07-30 10:28 ` Michael S. Tsirkin 2018-07-30 10:28 ` Michael S. Tsirkin 2018-07-30 11:18 ` Christoph Hellwig 2018-07-30 11:18 ` Christoph Hellwig 2018-07-30 13:26 ` Michael S. Tsirkin 2018-07-30 13:26 ` Michael S. Tsirkin 2018-07-31 17:30 ` Christoph Hellwig [this message] 2018-07-31 17:30 ` Christoph Hellwig 2018-07-31 20:36 ` Benjamin Herrenschmidt 2018-07-31 20:36 ` Benjamin Herrenschmidt 2018-08-01 8:16 ` Will Deacon 2018-08-01 8:16 ` Will Deacon 2018-08-01 8:36 ` Christoph Hellwig 2018-08-01 8:36 ` Christoph Hellwig 2018-08-01 8:36 ` Christoph Hellwig 2018-08-01 9:05 ` Will Deacon 2018-08-01 9:05 ` Will Deacon 2018-08-01 22:41 ` Michael S. Tsirkin 2018-08-01 22:41 ` Michael S. Tsirkin 2018-08-01 22:35 ` Michael S. Tsirkin 2018-08-01 22:35 ` Michael S. Tsirkin 2018-08-02 15:24 ` Benjamin Herrenschmidt 2018-08-02 15:24 ` Benjamin Herrenschmidt 2018-08-02 15:41 ` Michael S. Tsirkin 2018-08-02 15:41 ` Michael S. Tsirkin 2018-08-02 16:01 ` Benjamin Herrenschmidt 2018-08-02 16:01 ` Benjamin Herrenschmidt 2018-08-02 17:19 ` Michael S. Tsirkin 2018-08-02 17:19 ` Michael S. Tsirkin 2018-08-02 17:53 ` Benjamin Herrenschmidt 2018-08-02 17:53 ` Benjamin Herrenschmidt 2018-08-02 20:52 ` Michael S. Tsirkin 2018-08-02 20:52 ` Michael S. Tsirkin 2018-08-02 21:13 ` Benjamin Herrenschmidt 2018-08-02 21:13 ` Benjamin Herrenschmidt 2018-08-02 21:51 ` Michael S. Tsirkin 2018-08-02 21:51 ` Michael S. Tsirkin 2018-08-03 7:05 ` Christoph Hellwig 2018-08-03 7:05 ` Christoph Hellwig 2018-08-03 15:58 ` Benjamin Herrenschmidt 2018-08-03 15:58 ` Benjamin Herrenschmidt 2018-08-03 16:02 ` Christoph Hellwig 2018-08-03 16:02 ` Christoph Hellwig 2018-08-03 18:58 ` Benjamin Herrenschmidt 2018-08-03 18:58 ` Benjamin Herrenschmidt 2018-08-04 8:21 ` Christoph Hellwig 2018-08-04 8:21 ` Christoph Hellwig 2018-08-05 1:10 ` Benjamin Herrenschmidt 2018-08-05 1:10 ` Benjamin Herrenschmidt 2018-08-05 1:10 ` Benjamin Herrenschmidt 2018-08-05 7:29 ` Christoph Hellwig 2018-08-05 7:29 ` Christoph Hellwig 2018-08-05 21:16 ` Benjamin Herrenschmidt 2018-08-05 21:16 ` Benjamin Herrenschmidt 2018-08-05 21:30 ` Benjamin Herrenschmidt 2018-08-05 21:30 ` Benjamin Herrenschmidt 2018-08-06 9:42 ` Christoph Hellwig 2018-08-06 9:42 ` Christoph Hellwig 2018-08-06 19:52 ` Benjamin Herrenschmidt 2018-08-06 19:52 ` Benjamin Herrenschmidt 2018-08-07 6:21 ` Christoph Hellwig 2018-08-07 6:42 ` Benjamin Herrenschmidt 2018-08-07 6:42 ` Benjamin Herrenschmidt 2018-08-07 13:55 ` Christoph Hellwig 2018-08-07 20:32 ` Benjamin Herrenschmidt 2018-08-07 20:32 ` Benjamin Herrenschmidt 2018-08-08 6:31 ` Christoph Hellwig 2018-08-08 6:31 ` Christoph Hellwig 2018-08-08 10:07 ` Benjamin Herrenschmidt 2018-08-08 10:07 ` Benjamin Herrenschmidt 2018-08-08 12:30 ` Christoph Hellwig 2018-08-08 13:18 ` Benjamin Herrenschmidt 2018-08-08 13:18 ` Benjamin Herrenschmidt 2018-08-08 20:31 ` Michael S. Tsirkin 2018-08-08 22:13 ` Benjamin Herrenschmidt 2018-08-08 22:13 ` Benjamin Herrenschmidt 2018-08-09 2:00 ` Benjamin Herrenschmidt 2018-08-09 2:00 ` Benjamin Herrenschmidt 2018-08-09 5:40 ` Christoph Hellwig 2018-08-09 5:40 ` Christoph Hellwig 2018-09-07 0:09 ` Jiandi An 2018-09-10 6:19 ` Christoph Hellwig 2018-09-10 6:19 ` Christoph Hellwig 2018-09-10 8:53 ` Gerd Hoffmann 2018-09-10 8:53 ` Gerd Hoffmann 2018-08-08 20:31 ` Michael S. Tsirkin 2018-08-08 12:30 ` Christoph Hellwig 2018-08-07 13:55 ` Christoph Hellwig 2018-08-07 6:21 ` Christoph Hellwig 2018-08-03 19:07 ` Michael S. Tsirkin 2018-08-03 19:07 ` Michael S. Tsirkin 2018-08-04 1:11 ` Benjamin Herrenschmidt 2018-08-04 1:11 ` Benjamin Herrenschmidt 2018-08-04 1:16 ` Benjamin Herrenschmidt 2018-08-04 1:16 ` Benjamin Herrenschmidt 2018-08-05 0:22 ` Michael S. Tsirkin 2018-08-05 4:52 ` Benjamin Herrenschmidt 2018-08-05 4:52 ` Benjamin Herrenschmidt 2018-08-06 13:46 ` Michael S. Tsirkin 2018-08-06 19:56 ` Benjamin Herrenschmidt 2018-08-06 19:56 ` Benjamin Herrenschmidt 2018-08-06 20:35 ` Michael S. Tsirkin 2018-08-06 21:26 ` Benjamin Herrenschmidt 2018-08-06 21:26 ` Benjamin Herrenschmidt 2018-08-06 21:46 ` Michael S. Tsirkin 2018-08-06 21:46 ` Michael S. Tsirkin 2018-08-06 22:13 ` Benjamin Herrenschmidt 2018-08-06 22:13 ` Benjamin Herrenschmidt 2018-08-06 23:16 ` Benjamin Herrenschmidt 2018-08-06 23:16 ` Benjamin Herrenschmidt 2018-08-06 23:45 ` Michael S. Tsirkin 2018-08-07 0:18 ` Benjamin Herrenschmidt 2018-08-07 0:18 ` Benjamin Herrenschmidt 2018-08-07 6:32 ` Christoph Hellwig 2018-08-07 6:32 ` Christoph Hellwig 2018-08-06 23:45 ` Michael S. Tsirkin 2018-08-07 6:27 ` Christoph Hellwig 2018-08-07 6:27 ` Christoph Hellwig 2018-08-07 6:44 ` Benjamin Herrenschmidt 2018-08-07 6:44 ` Benjamin Herrenschmidt 2018-08-07 6:18 ` Christoph Hellwig 2018-08-07 6:18 ` Christoph Hellwig 2018-08-07 6:16 ` Christoph Hellwig 2018-08-07 6:16 ` Christoph Hellwig 2018-08-06 23:18 ` Benjamin Herrenschmidt 2018-08-06 23:18 ` Benjamin Herrenschmidt 2018-08-07 6:12 ` Christoph Hellwig 2018-08-07 6:12 ` Christoph Hellwig 2018-08-06 20:35 ` Michael S. Tsirkin 2018-08-06 13:46 ` Michael S. Tsirkin 2018-08-05 0:22 ` Michael S. Tsirkin 2018-08-04 1:18 ` Benjamin Herrenschmidt 2018-08-04 1:18 ` Benjamin Herrenschmidt 2018-08-04 1:22 ` Benjamin Herrenschmidt 2018-08-04 1:22 ` Benjamin Herrenschmidt 2018-08-05 0:23 ` Michael S. Tsirkin 2018-08-05 0:23 ` Michael S. Tsirkin 2018-08-03 19:17 ` Michael S. Tsirkin 2018-08-03 19:17 ` Michael S. Tsirkin 2018-08-04 8:15 ` Christoph Hellwig 2018-08-04 8:15 ` Christoph Hellwig 2018-08-05 0:09 ` Michael S. Tsirkin 2018-08-05 0:09 ` Michael S. Tsirkin 2018-08-05 1:11 ` Benjamin Herrenschmidt 2018-08-05 1:11 ` Benjamin Herrenschmidt 2018-08-05 7:25 ` Christoph Hellwig 2018-08-05 7:25 ` Christoph Hellwig 2018-08-05 0:53 ` Benjamin Herrenschmidt 2018-08-05 0:53 ` Benjamin Herrenschmidt 2018-08-05 0:27 ` Michael S. Tsirkin 2018-08-05 0:27 ` Michael S. Tsirkin 2018-08-06 14:05 ` Will Deacon 2018-08-06 14:05 ` Will Deacon 2018-08-01 21:56 ` Michael S. Tsirkin 2018-08-01 21:56 ` Michael S. Tsirkin 2018-08-02 15:33 ` Benjamin Herrenschmidt 2018-08-02 15:33 ` Benjamin Herrenschmidt 2018-08-02 20:53 ` Michael S. Tsirkin 2018-08-03 7:06 ` Christoph Hellwig 2018-08-03 7:06 ` Christoph Hellwig 2018-08-02 20:53 ` Michael S. Tsirkin 2018-08-02 20:55 ` Michael S. Tsirkin 2018-08-02 20:55 ` Michael S. Tsirkin 2018-08-03 2:41 ` Jason Wang 2018-08-03 2:41 ` Jason Wang 2018-08-03 19:08 ` Michael S. Tsirkin 2018-08-04 1:21 ` Benjamin Herrenschmidt 2018-08-04 1:21 ` Benjamin Herrenschmidt 2018-08-05 0:24 ` Michael S. Tsirkin 2018-08-05 0:24 ` Michael S. Tsirkin 2018-08-06 9:02 ` Anshuman Khandual 2018-08-06 9:02 ` Anshuman Khandual 2018-08-06 13:36 ` Michael S. Tsirkin 2018-08-06 13:36 ` Michael S. Tsirkin 2018-08-06 15:24 ` Christoph Hellwig 2018-08-06 16:06 ` Michael S. Tsirkin 2018-08-06 16:06 ` Michael S. Tsirkin 2018-08-06 16:10 ` Christoph Hellwig 2018-08-06 16:10 ` Christoph Hellwig 2018-08-06 16:13 ` Michael S. Tsirkin 2018-08-06 16:13 ` Michael S. Tsirkin 2018-08-06 16:34 ` Christoph Hellwig 2018-08-06 16:34 ` Christoph Hellwig 2018-08-06 15:24 ` Christoph Hellwig 2018-08-03 19:08 ` Michael S. Tsirkin 2018-07-20 3:59 Anshuman Khandual
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=20180731173052.GA17153@infradead.org \ --to=hch@infradead.org \ --cc=aik@ozlabs.ru \ --cc=benh@kernel.crashing.org \ --cc=david@gibson.dropbear.id.au \ --cc=elfring@users.sourceforge.net \ --cc=haren@linux.vnet.ibm.com \ --cc=jasowang@redhat.com \ --cc=jean-philippe.brucker@arm.com \ --cc=joe@perches.com \ --cc=khandual@linux.vnet.ibm.com \ --cc=linux-kernel@vger.kernel.org \ --cc=linuxppc-dev@lists.ozlabs.org \ --cc=linuxram@us.ibm.com \ --cc=marc.zyngier@arm.com \ --cc=mpe@ellerman.id.au \ --cc=mst@redhat.com \ --cc=paulus@samba.org \ --cc=robh@kernel.org \ --cc=robin.murphy@arm.com \ --cc=srikar@linux.vnet.ibm.com \ --cc=virtualization@lists.linux-foundation.org \ --cc=will.deacon@arm.com \ /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: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.