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From: Cornelia Huck <cohuck@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-nvdimm@lists.01.org,
	miklos@szeredi.hu, stefanha@redhat.com, dgilbert@redhat.com,
	swhiteho@redhat.com, Sebastian Ott <sebott@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Collin Walling <walling@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v2 18/30] virtio_fs, dax: Set up virtio_fs dax_device
Date: Thu, 18 Jul 2019 16:47:07 +0200
Message-ID: <20190718164707.76d60fdc.cohuck@redhat.com> (raw)
In-Reply-To: <20190718132049.37bea675.pasic@linux.ibm.com>

On Thu, 18 Jul 2019 13:20:49 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu, 18 Jul 2019 11:04:17 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > On Wed, 17 Jul 2019 19:27:25 +0200
> > Halil Pasic <pasic@linux.ibm.com> wrote:

> > > I'm trying to figure out how is this supposed to work on s390. My concern
> > > is, that on s390 PCI memory needs to be accessed by special
> > > instructions. This is taken care of by the stuff defined in
> > > arch/s390/include/asm/io.h. E.g. we 'override' __raw_writew so it uses
> > > the appropriate s390 instruction. However if the code does not use the
> > > linux abstractions for accessing PCI memory, but assumes it can be
> > > accessed like RAM, we have a problem.
> > > 
> > > Looking at this patch, it seems to me, that we might end up with exactly
> > > the case described. For example AFAICT copy_to_iter() (3) resolves to
> > > the function in lib/iov_iter.c which does not seem to cater for s390
> > > oddities.  
> > 
> > What about the new pci instructions recently introduced? Not sure how
> > they differ from the old ones (which are currently the only ones
> > supported in QEMU...), but I'm pretty sure they are supposed to solve
> > an issue :)
> >   
> 
> I'm struggling to find the connection between this topic and the new pci
> instructions. Can you please explain in more detail?

The problem is that I'm lacking detail myself... if the new approach is
handling some things substantially differently (e.g. you set up
something and then do read/writes instead of going through
instructions), things will probably work out differently.

> 
> > > 
> > > I didn't have the time to investigate this properly, and since virtio-fs
> > > is virtual, we may be able to get around what is otherwise a
> > > limitation on s390. My understanding of these areas is admittedly
> > > shallow, and since I'm not sure I'll have much more time to
> > > invest in the near future I decided to raise concern.
> > > 
> > > Any opinions?  
> > 
> > Let me point to the thread starting at
> > https://marc.info/?l=linux-s390&m=155048406205221&w=2 as well. That
> > memory region stuff is still unsolved for ccw, and I'm not sure if we
> > need to do something for zpci as well.
> >   
> 
> Right virtio-ccw is another problem, but at least there we don't have the
> need to limit ourselves to a very specific set of instructions (for
> accessing memory).
> 
> zPCI i.e. virtio-pci on z should require much less dedicated love if any

s/virtio-pci/pci/

> at all. Unfortunately I'm not very knowledgeable on either PCI in general
> or its s390 variant.

Right, the biggest issue with zpci and shared regions is the
interaction with ccw using shared regions as well.

Unfortunately, I can't judge any zpci details from here, either :(

If virtio-fs is working in its non-dax version, we'll at least have
something on s390. (Has anyone tried that, btw?) It seems that s390 is
only supporting a limited subset of dax anyway.

  reply index

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-15 19:26 [PATCH v2 00/30] [RFC] virtio-fs: shared file system for virtual machines Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 01/30] fuse: delete dentry if timeout is zero Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 02/30] fuse: Clear setuid bit even in cache=never path Vivek Goyal
2019-05-20 14:41   ` Miklos Szeredi
2019-05-20 14:44     ` Miklos Szeredi
2019-05-20 20:25       ` Nikolaus Rath
2019-05-21 15:01     ` Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 03/30] fuse: Use default_file_splice_read for direct IO Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 04/30] fuse: export fuse_end_request() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 05/30] fuse: export fuse_len_args() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 06/30] fuse: Export fuse_send_init_request() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 07/30] fuse: export fuse_get_unique() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 08/30] fuse: extract fuse_fill_super_common() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 09/30] fuse: add fuse_iqueue_ops callbacks Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 10/30] fuse: Separate fuse device allocation and installation in fuse_conn Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 11/30] virtio_fs: add skeleton virtio_fs.ko module Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 12/30] dax: remove block device dependencies Vivek Goyal
2019-05-16  0:21   ` Dan Williams
2019-05-16 10:07     ` Stefan Hajnoczi
2019-05-16 14:23     ` Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 13/30] dax: Pass dax_dev to dax_writeback_mapping_range() Vivek Goyal
2019-05-15 19:26 ` [PATCH v2 14/30] virtio: Add get_shm_region method Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 15/30] virtio: Implement get_shm_region for PCI transport Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 16/30] virtio: Implement get_shm_region for MMIO transport Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 17/30] fuse, dax: add fuse_conn->dax_dev field Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 18/30] virtio_fs, dax: Set up virtio_fs dax_device Vivek Goyal
2019-07-17 17:27   ` Halil Pasic
2019-07-18  9:04     ` Cornelia Huck
2019-07-18 11:20       ` Halil Pasic
2019-07-18 14:47         ` Cornelia Huck [this message]
2019-07-18 13:15     ` Vivek Goyal
2019-07-18 14:30       ` Dan Williams
2019-07-22 10:51         ` Christian Borntraeger
2019-07-22 10:56           ` Dr. David Alan Gilbert
2019-07-22 11:20             ` Christian Borntraeger
2019-07-22 11:43               ` Cornelia Huck
2019-07-22 12:00                 ` Christian Borntraeger
2019-07-22 12:08                   ` David Hildenbrand
2019-07-29 13:20                     ` Stefan Hajnoczi
2019-05-15 19:27 ` [PATCH v2 19/30] fuse: Keep a list of free dax memory ranges Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 20/30] fuse: Introduce setupmapping/removemapping commands Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 21/30] fuse, dax: Implement dax read/write operations Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 22/30] fuse, dax: add DAX mmap support Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 23/30] fuse: Define dax address space operations Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 24/30] fuse, dax: Take ->i_mmap_sem lock during dax page fault Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 25/30] fuse: Maintain a list of busy elements Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 26/30] fuse: Add logic to free up a memory range Vivek Goyal
     [not found]   ` <CAN+Pk99SNKSf+GjSQUUWt_eu1fSjTy_ByUOEQUXHi8zNqXY1zA@mail.gmail.com>
2019-05-20 12:53     ` Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 27/30] fuse: Release file in process context Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 28/30] fuse: Reschedule dax free work if too many EAGAIN attempts Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 29/30] fuse: Take inode lock for dax inode truncation Vivek Goyal
2019-05-15 19:27 ` [PATCH v2 30/30] virtio-fs: Do not provide abort interface in fusectl Vivek Goyal

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