On Thu, 18 Jul 2019 11:04:17 +0200 Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > On Wed, 17 Jul 2019 19:27:25 +0200 > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > On Wed, 15 May 2019 15:27:03 -0400 > > Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > > > From: Stefan Hajnoczi <stefanha@xxxxxxxxxx> > > > > > > Setup a dax device. > > > > > > Use the shm capability to find the cache entry and map it. > > > > > > The DAX window is accessed by the fs/dax.c infrastructure and must have > > > struct pages (at least on x86). Use devm_memremap_pages() to map the > > > DAX window PCI BAR and allocate struct page. > > > > > > > Sorry for being this late. I don't see any more recent version so I will > > comment here. > > [Yeah, this one has been sitting in my to-review queue far too long as > well :(] > > > > > 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? > > > > 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 at all. Unfortunately I'm not very knowledgeable on either PCI in general or its s390 variant. > Does s390 work with DAX at all? ISTR that DAX evolved from XIP, so I > thought it did? > Documentation/filesystems/dax.txt even mentions dcssblk: s390 dcss block device driver as a source of inspiration. So I suppose it does work. Regards, Halil > > > > [CCing some s390 people who are probably more knowledgeable than my > > on these matters.] > > > > Regards, > > Halil > > > > > > > Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx> > > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> > > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> > > > Signed-off-by: Sebastien Boeuf <sebastien.boeuf@xxxxxxxxx> > > > Signed-off-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> > > > --- > > > > [..] > > > > > +/* Map a window offset to a page frame number. The window offset > > > will have > > > + * been produced by .iomap_begin(), which maps a file offset to a > > > window > > > + * offset. > > > + */ > > > +static long virtio_fs_direct_access(struct dax_device *dax_dev, > > > pgoff_t pgoff, > > > + long nr_pages, void **kaddr, > > > pfn_t *pfn) +{ > > > + struct virtio_fs *fs = dax_get_private(dax_dev); > > > + phys_addr_t offset = PFN_PHYS(pgoff); > > > + size_t max_nr_pages = fs->window_len/PAGE_SIZE - pgoff; > > > + > > > + if (kaddr) > > > + *kaddr = fs->window_kaddr + offset; > > > > (2) Here we use fs->window_kaddr, basically directing the access to > > the virtio shared memory region. > > > > > + if (pfn) > > > + *pfn = phys_to_pfn_t(fs->window_phys_addr + > > > offset, > > > + PFN_DEV | PFN_MAP); > > > + return nr_pages > max_nr_pages ? max_nr_pages : nr_pages; > > > +} > > > + > > > +static size_t virtio_fs_copy_from_iter(struct dax_device *dax_dev, > > > + pgoff_t pgoff, void *addr, > > > + size_t bytes, struct > > > iov_iter *i) +{ > > > + return copy_from_iter(addr, bytes, i); > > > +} > > > + > > > +static size_t virtio_fs_copy_to_iter(struct dax_device *dax_dev, > > > + pgoff_t pgoff, void *addr, > > > + size_t bytes, struct > > > iov_iter *i) +{ > > > + return copy_to_iter(addr, bytes, i); > > > > (3) And this should be the access to it. Which does not seem to use. > > > > > +} > > > + > > > +static const struct dax_operations virtio_fs_dax_ops = { > > > + .direct_access = virtio_fs_direct_access, > > > + .copy_from_iter = virtio_fs_copy_from_iter, > > > + .copy_to_iter = virtio_fs_copy_to_iter, > > > +}; > > > + > > > +static void virtio_fs_percpu_release(struct percpu_ref *ref) > > > +{ > > > + struct virtio_fs_memremap_info *mi = > > > + container_of(ref, struct virtio_fs_memremap_info, > > > ref); + > > > + complete(&mi->completion); > > > +} > > > + > > > +static void virtio_fs_percpu_exit(void *data) > > > +{ > > > + struct virtio_fs_memremap_info *mi = data; > > > + > > > + wait_for_completion(&mi->completion); > > > + percpu_ref_exit(&mi->ref); > > > +} > > > + > > > +static void virtio_fs_percpu_kill(struct percpu_ref *ref) > > > +{ > > > + percpu_ref_kill(ref); > > > +} > > > + > > > +static void virtio_fs_cleanup_dax(void *data) > > > +{ > > > + struct virtio_fs *fs = data; > > > + > > > + kill_dax(fs->dax_dev); > > > + put_dax(fs->dax_dev); > > > +} > > > + > > > +static int virtio_fs_setup_dax(struct virtio_device *vdev, struct > > > virtio_fs *fs) +{ > > > + struct virtio_shm_region cache_reg; > > > + struct virtio_fs_memremap_info *mi; > > > + struct dev_pagemap *pgmap; > > > + bool have_cache; > > > + int ret; > > > + > > > + if (!IS_ENABLED(CONFIG_DAX_DRIVER)) > > > + return 0; > > > + > > > + /* Get cache region */ > > > + have_cache = virtio_get_shm_region(vdev, > > > + &cache_reg, > > > + > > > (u8)VIRTIO_FS_SHMCAP_ID_CACHE); > > > + if (!have_cache) { > > > + dev_err(&vdev->dev, "%s: No cache capability\n", > > > __func__); > > > + return -ENXIO; > > > + } else { > > > + dev_notice(&vdev->dev, "Cache len: 0x%llx @ > > > 0x%llx\n", > > > + cache_reg.len, cache_reg.addr); > > > + } > > > + > > > + mi = devm_kzalloc(&vdev->dev, sizeof(*mi), GFP_KERNEL); > > > + if (!mi) > > > + return -ENOMEM; > > > + > > > + init_completion(&mi->completion); > > > + ret = percpu_ref_init(&mi->ref, virtio_fs_percpu_release, > > > 0, > > > + GFP_KERNEL); > > > + if (ret < 0) { > > > + dev_err(&vdev->dev, "%s: percpu_ref_init failed > > > (%d)\n", > > > + __func__, ret); > > > + return ret; > > > + } > > > + > > > + ret = devm_add_action(&vdev->dev, virtio_fs_percpu_exit, > > > mi); > > > + if (ret < 0) { > > > + percpu_ref_exit(&mi->ref); > > > + return ret; > > > + } > > > + > > > + pgmap = &mi->pgmap; > > > + pgmap->altmap_valid = false; > > > + pgmap->ref = &mi->ref; > > > + pgmap->kill = virtio_fs_percpu_kill; > > > + pgmap->type = MEMORY_DEVICE_FS_DAX; > > > + > > > + /* Ideally we would directly use the PCI BAR resource but > > > + * devm_memremap_pages() wants its own copy in pgmap. So > > > + * initialize a struct resource from scratch (only the > > > start > > > + * and end fields will be used). > > > + */ > > > + pgmap->res = (struct resource){ > > > + .name = "virtio-fs dax window", > > > + .start = (phys_addr_t) cache_reg.addr, > > > + .end = (phys_addr_t) cache_reg.addr + > > > cache_reg.len - 1, > > > + }; > > > + > > > + fs->window_kaddr = devm_memremap_pages(&vdev->dev, > > > pgmap); > > > > (1) Here we assign fs->window_kaddr basically from the virtio shm > > region. > > > > > + if (IS_ERR(fs->window_kaddr)) > > > + return PTR_ERR(fs->window_kaddr); > > > + > > > + fs->window_phys_addr = (phys_addr_t) cache_reg.addr; > > > + fs->window_len = (phys_addr_t) cache_reg.len; > > > + > > > + dev_dbg(&vdev->dev, "%s: window kaddr 0x%px phys_addr > > > 0x%llx" > > > + " len 0x%llx\n", __func__, fs->window_kaddr, > > > cache_reg.addr, > > > + cache_reg.len); > > > + > > > + fs->dax_dev = alloc_dax(fs, NULL, &virtio_fs_dax_ops); > > > + if (!fs->dax_dev) > > > + return -ENOMEM; > > > + > > > + return devm_add_action_or_reset(&vdev->dev, > > > virtio_fs_cleanup_dax, fs); +} > > > + > > > > [..] > > >
