LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Stefan Hajnoczi <stefanha@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Vivek Goyal <vgoyal@redhat.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, miklos@szeredi.hu, sweil@redhat.com,
	swhiteho@redhat.com
Subject: Re: [PATCH 18/52] virtio-fs: Map cache using the values from the capabilities
Date: Wed, 2 Jan 2019 10:24:55 +0000
Message-ID: <20190102102455.GF24009@stefanha-x1.localdomain> (raw)
In-Reply-To: <4a870d9c-8c46-7f2e-4947-a3913a824d14@redhat.com>

[-- Attachment #1: Type: text/plain, Size: 4874 bytes --]

On Tue, Dec 18, 2018 at 06:25:27PM +0100, David Hildenbrand wrote:
> On 18.12.18 18:13, Cornelia Huck wrote:
> > On Mon, 17 Dec 2018 14:56:38 +0000
> > Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > 
> >> On Mon, Dec 17, 2018 at 11:53:46AM +0100, David Hildenbrand wrote:
> >>> On 14.12.18 14:44, Stefan Hajnoczi wrote:  
> >>>> On Thu, Dec 13, 2018 at 01:38:23PM +0100, Cornelia Huck wrote:  
> >>>>> On Thu, 13 Dec 2018 13:24:31 +0100
> >>>>> David Hildenbrand <david@redhat.com> wrote:
> > 
> >>>>>> As s390x does not have the concept of memory mapped io (RAM is RAM,
> >>>>>> nothing else), this is not architectured. vitio-ccw can therefore not
> >>>>>> define anything similar like that. However, in virtual environments we
> >>>>>> can do whatever we want on top of the pure transport (e.g. on the virtio
> >>>>>> layer).
> >>>>>>
> >>>>>> Conny can correct me if I am wrong.  
> >>>>>
> >>>>> I don't think you're wrong, but I haven't read the code yet and I'm
> >>>>> therefore not aware of the purpose of this BAR.
> >>>>>
> >>>>> Generally, if there is a memory location shared between host and guest,
> >>>>> we need a way to communicate its location, which will likely differ
> >>>>> between transports. For ccw, I could imagine a new channel command
> >>>>> dedicated to exchanging configuration information (similar to what
> >>>>> exists today to communicate the locations of virtqueues), but I'd
> >>>>> rather not go down this path.
> >>>>>
> >>>>> Without reading the code/design further, can we use one of the
> >>>>> following instead of a BAR:
> >>>>> - a virtqueue;
> >>>>> - something in config space?
> >>>>> That would be implementable by any virtio transport.  
> >>>>
> >>>> The way I think about this is that we wish to extend the VIRTIO device
> >>>> model with the concept of shared memory.  virtio-fs, virtio-gpu, and
> >>>> virtio-vhost-user all have requirements for shared memory.
> >>>>
> >>>> This seems like a transport-level issue to me.  PCI supports
> >>>> memory-mapped I/O and that's the right place to do it.  If you try to
> >>>> put it into config space or the virtqueue, you'll end up with something
> >>>> that cannot be realized as a PCI device because it bypasses PCI bus
> >>>> address translation.
> >>>>
> >>>> If CCW needs a side-channel, that's fine.  But that side-channel is a
> >>>> CCW-specific mechanism and probably doesn't apply to all other
> >>>> transports.
> >>>>
> >>>> Stefan
> >>>>   
> >>>
> >>> I think the problem is more fundamental. There is no iommu. Whatever
> >>> shared region you want to indicate, you want it to be assigned a memory
> >>> region in guest physical memory. Like a DIMM/NVDIMM. And this should be
> >>> different to the concept of a BAR. Or am I missing something?  
> >>
> >> If you implement a physical virtio PCI adapter then there is bus
> >> addressing and an IOMMU and VIRTIO has support for that.  I'm not sure I
> >> understand what you mean by "there is no iommu"?
> > 
> > For ccw, there is no iommu; channel-program translation is doing
> > similar things. (I hope that is what David meant :)
> > 
> >>
> >>> I am ok with using whatever other channel to transport such information.
> >>> But I believe this is different to a typical BAR. (I wish I knew more
> >>> about PCI internals ;) ).
> >>>
> >>> I would also like to know how shared memory works as of now for e.g.
> >>> virtio-gpu.  
> >>
> >> virtio-gpu currently does not use shared memory, it needs it for future
> >> features.
> > 
> > OK, that all sounds like we need to define a generic, per transport,
> > device agnostic way to specify shared memory.
> > 
> > Where is that memory situated? Is it something in guest memory (like
> > virtqueues)? If it is something provided by the device, things will get
> > tricky for ccw (remember that there's no mmio on s390; pci on s390 uses
> > special instructions for that.)
> > 
> 
> I am just very very confused right now. What I am struggling with right
> now (Stefan, hope you can clarify it for me):
> 
> We need some place where this shared memory is located in the guest
> physical memory. On x86 - if I am not wrong - this BAR is placed into
> the reserved memory area between 3 and 4 GB.

Right, the shared memory is provided by the device and does not live in
guest RAM.

> There is no such thing on
> s390x. Because we don't have IO via memory (yet). All we have is one or
> two KVM memory slots filled with all memory.
> 
> So what we will need on s390x is on the QEMU side such a reserved memory
> region where devices like virtio-fs can reserve a region for shared memory.
> 
> So it is something like a dimm/nvdimm except that it is smaller and not
> visible to the user directly (via memory backends).

I see.  That makes sense.

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 455 bytes --]

  reply index

Thread overview: 98+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-10 17:12 [PATCH 00/52] [RFC] virtio-fs: shared file system for virtual machines Vivek Goyal
2018-12-10 17:12 ` [PATCH 01/52] fuse: add skeleton virtio_fs.ko module Vivek Goyal
2018-12-10 17:12 ` [PATCH 02/52] fuse: add probe/remove virtio driver Vivek Goyal
2018-12-10 17:12 ` [PATCH 03/52] fuse: rely on mutex_unlock() barrier instead of fput() Vivek Goyal
2018-12-10 17:12 ` [PATCH 04/52] fuse: extract fuse_fill_super_common() Vivek Goyal
2018-12-10 17:12 ` [PATCH 05/52] virtio_fs: get mount working Vivek Goyal
2018-12-10 17:12 ` [PATCH 06/52] fuse: export fuse_end_request() Vivek Goyal
2018-12-10 17:12 ` [PATCH 07/52] fuse: export fuse_len_args() Vivek Goyal
2018-12-10 17:12 ` [PATCH 08/52] fuse: add fuse_iqueue_ops callbacks Vivek Goyal
2018-12-10 17:12 ` [PATCH 09/52] fuse: process requests queues Vivek Goyal
2018-12-10 17:12 ` [PATCH 10/52] fuse: export fuse_get_unique() Vivek Goyal
2018-12-10 17:12 ` [PATCH 11/52] fuse: implement FUSE_FORGET for virtio-fs Vivek Goyal
2018-12-10 17:12 ` [PATCH 12/52] virtio_fs: Set up dax_device Vivek Goyal
2018-12-10 17:12 ` [PATCH 13/52] dax: remove block device dependencies Vivek Goyal
2018-12-10 17:12 ` [PATCH 14/52] fuse: add fuse_conn->dax_dev field Vivek Goyal
2018-12-10 17:12 ` [PATCH 15/52] fuse: map virtio_fs DAX window BAR Vivek Goyal
2018-12-12 16:37   ` Christian Borntraeger
2018-12-13 11:55     ` Stefan Hajnoczi
2018-12-13 16:06   ` kbuild test robot
2018-12-13 19:55   ` Dan Williams
2018-12-13 20:09     ` Dr. David Alan Gilbert
2018-12-13 20:15       ` Dan Williams
2018-12-13 20:40         ` Vivek Goyal
2018-12-13 21:18           ` Vivek Goyal
2018-12-14 10:09             ` Dr. David Alan Gilbert
2018-12-10 17:12 ` [PATCH 16/52] virtio-fs: Add VIRTIO_PCI_CAP_SHARED_MEMORY_CFG and utility to find them Vivek Goyal
2018-12-12 16:36   ` [PATCH] virtio-fs: fix semicolon.cocci warnings kbuild test robot
2018-12-12 16:36   ` [PATCH 16/52] virtio-fs: Add VIRTIO_PCI_CAP_SHARED_MEMORY_CFG and utility to find them kbuild test robot
2018-12-10 17:12 ` [PATCH 17/52] virtio-fs: Retrieve shm capabilities for cache Vivek Goyal
2018-12-10 17:12 ` [PATCH 18/52] virtio-fs: Map cache using the values from the capabilities Vivek Goyal
2018-12-13  9:10   ` David Hildenbrand
2018-12-13  9:13     ` Dr. David Alan Gilbert
2018-12-13  9:34       ` David Hildenbrand
2018-12-13 10:00         ` Dr. David Alan Gilbert
2018-12-13 11:26           ` David Hildenbrand
2018-12-13 12:15             ` Dr. David Alan Gilbert
2018-12-13 12:24               ` David Hildenbrand
2018-12-13 12:38                 ` Cornelia Huck
2018-12-14 13:44                   ` Stefan Hajnoczi
2018-12-14 13:50                     ` Cornelia Huck
2018-12-14 14:06                       ` Dr. David Alan Gilbert
2018-12-17 11:25                       ` Stefan Hajnoczi
2018-12-17 10:53                     ` David Hildenbrand
2018-12-17 14:56                       ` Stefan Hajnoczi
2018-12-18 17:13                         ` Cornelia Huck
2018-12-18 17:25                           ` David Hildenbrand
2019-01-02 10:24                             ` Stefan Hajnoczi [this message]
2019-03-17  0:33   ` Liu Bo
2019-03-20 10:42     ` Dr. David Alan Gilbert
2019-03-17  0:35   ` [PATCH] virtio-fs: fix multiple tag support Liu Bo
2019-03-19 20:26     ` Vivek Goyal
2019-03-20  2:04       ` Liu Bo
2018-12-10 17:12 ` [PATCH 19/52] virito-fs: Make dax optional Vivek Goyal
2018-12-10 17:12 ` [PATCH 20/52] Limit number of pages returned by direct_access() Vivek Goyal
2018-12-10 17:12 ` [PATCH 21/52] fuse: Introduce fuse_dax_mapping Vivek Goyal
2018-12-10 17:12 ` [PATCH 22/52] Create a list of free memory ranges Vivek Goyal
2018-12-11 17:44   ` kbuild test robot
2018-12-15 19:22   ` kbuild test robot
2018-12-10 17:12 ` [PATCH 23/52] fuse: simplify fuse_fill_super_common() calling Vivek Goyal
2018-12-10 17:12 ` [PATCH 24/52] fuse: Introduce setupmapping/removemapping commands Vivek Goyal
2018-12-10 17:12 ` [PATCH 25/52] Introduce interval tree basic data structures Vivek Goyal
2018-12-10 17:12 ` [PATCH 26/52] fuse: Implement basic DAX read/write support commands Vivek Goyal
2018-12-10 17:12 ` [PATCH 27/52] fuse: Maintain a list of busy elements Vivek Goyal
2018-12-10 17:12 ` [PATCH 28/52] Do fallocate() to grow file before mapping for file growing writes Vivek Goyal
2018-12-11  6:13   ` kbuild test robot
2018-12-11  6:20   ` kbuild test robot
2018-12-10 17:12 ` [PATCH 29/52] fuse: add DAX mmap support Vivek Goyal
2018-12-10 17:12 ` [PATCH 30/52] fuse: delete dentry if timeout is zero Vivek Goyal
2018-12-10 17:12 ` [PATCH 31/52] dax: Pass dax_dev to dax_writeback_mapping_range() Vivek Goyal
2018-12-11  6:12   ` kbuild test robot
2018-12-11 17:38   ` kbuild test robot
2018-12-10 17:12 ` [PATCH 32/52] fuse: Define dax address space operations Vivek Goyal
2018-12-10 17:12 ` [PATCH 33/52] fuse, dax: Take ->i_mmap_sem lock during dax page fault Vivek Goyal
2018-12-10 17:13 ` [PATCH 34/52] fuse: Add logic to free up a memory range Vivek Goyal
2018-12-10 17:13 ` [PATCH 35/52] fuse: Add logic to do direct reclaim of memory Vivek Goyal
2018-12-10 17:13 ` [PATCH 36/52] fuse: Kick worker when free memory drops below 20% of total ranges Vivek Goyal
2018-12-10 17:13 ` [PATCH 37/52] fuse: multiplex cached/direct_io/dax file operations Vivek Goyal
2018-12-10 17:13 ` [PATCH 38/52] Dispatch FORGET requests later instead of dropping them Vivek Goyal
2018-12-10 17:13 ` [PATCH 39/52] Release file in process context Vivek Goyal
2018-12-10 17:13 ` [PATCH 40/52] fuse: Do not block on inode lock while freeing memory range Vivek Goyal
2018-12-10 17:13 ` [PATCH 41/52] fuse: Reschedule dax free work if too many EAGAIN attempts Vivek Goyal
2018-12-10 17:13 ` [PATCH 42/52] fuse: Wait for memory ranges to become free Vivek Goyal
2018-12-10 17:13 ` [PATCH 43/52] fuse: Take inode lock for dax inode truncation Vivek Goyal
2018-12-10 17:13 ` [PATCH 44/52] fuse: Clear setuid bit even in direct I/O path Vivek Goyal
2018-12-10 17:13 ` [PATCH 45/52] virtio: Free fuse devices on umount Vivek Goyal
2018-12-10 17:13 ` [PATCH 46/52] virtio-fs: Retrieve shm capabilities for version table Vivek Goyal
2018-12-10 17:13 ` [PATCH 47/52] virtio-fs: Map using the values from the capabilities Vivek Goyal
2018-12-10 17:13 ` [PATCH 48/52] virtio-fs: pass version table pointer to fuse Vivek Goyal
2018-12-10 17:13 ` [PATCH 49/52] fuse: don't crash if version table is NULL Vivek Goyal
2018-12-10 17:13 ` [PATCH 50/52] fuse: add shared version support (virtio-fs only) Vivek Goyal
2018-12-10 17:13 ` [PATCH 51/52] fuse: shared version cleanups Vivek Goyal
2018-12-10 17:13 ` [PATCH 52/52] fuse: fix fuse_permission() for the default_permissions case Vivek Goyal
2018-12-19 21:25   ` kbuild test robot
2018-12-11 12:54 ` [PATCH 00/52] [RFC] virtio-fs: shared file system for virtual machines Stefan Hajnoczi
2018-12-12 20:30 ` Konrad Rzeszutek Wilk
2018-12-12 21:22   ` Vivek Goyal
2019-02-12 15:56 ` Aneesh Kumar K.V
2019-02-12 18:57   ` Vivek Goyal

Reply instructions:

You may reply publically 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=20190102102455.GF24009@stefanha-x1.localdomain \
    --to=stefanha@redhat.com \
    --cc=cohuck@redhat.com \
    --cc=david@redhat.com \
    --cc=dgilbert@redhat.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=miklos@szeredi.hu \
    --cc=sweil@redhat.com \
    --cc=swhiteho@redhat.com \
    --cc=vgoyal@redhat.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: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox