Hi Dan, On 02/04/18 15:05 -0800, Dan Williams wrote: > Filesystem-DAX is incompatible with 'longterm' page pinning. Without > page cache indirection a DAX mapping maps filesystem blocks directly. > This means that the filesystem must not modify a file's block map while > any page in a mapping is pinned. In order to prevent the situation of > userspace holding of filesystem operations indefinitely, disallow > 'longterm' Filesystem-DAX mappings. > > RDMA has the same conflict and the plan there is to add a 'with lease' > mechanism to allow the kernel to notify userspace that the mapping is > being torn down for block-map maintenance. Perhaps something similar can > be put in place for vfio. > > Note that xfs and ext4 still report: > > "DAX enabled. Warning: EXPERIMENTAL, use at your own risk" > > ...at mount time, and resolving the dax-dma-vs-truncate problem is one > of the last hurdles to remove that designation. > > Cc: Alex Williamson <alex.william...@redhat.com> > Cc: Michal Hocko <mho...@suse.com> > Cc: Christoph Hellwig <h...@lst.de> > Cc: k...@vger.kernel.org > Cc: <sta...@vger.kernel.org> > Reported-by: Haozhong Zhang <haozhong.zh...@intel.com> > Fixes: d475c6346a38 ("dax,ext2: replace XIP read and write with DAX I/O") > Signed-off-by: Dan Williams <dan.j.willi...@intel.com> > --- > drivers/vfio/vfio_iommu_type1.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index e30e29ae4819..45657e2b1ff7 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -338,11 +338,12 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned > long vaddr, > { > struct page *page[1]; > struct vm_area_struct *vma; > + struct vm_area_struct *vmas[1]; > int ret; > > if (mm == current->mm) { > - ret = get_user_pages_fast(vaddr, 1, !!(prot & IOMMU_WRITE), > - page); > + ret = get_user_pages_longterm(vaddr, 1, !!(prot & IOMMU_WRITE), > + page, vmas); > } else { > unsigned int flags = 0; > > @@ -351,7 +352,18 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned > long vaddr, > > down_read(&mm->mmap_sem); > ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > - NULL, NULL); > + vmas, NULL); > + /* > + * The lifetime of a vaddr_get_pfn() page pin is > + * userspace-controlled. In the fs-dax case this could > + * lead to indefinite stalls in filesystem operations. > + * Disallow attempts to pin fs-dax pages via this > + * interface. > + */ > + if (ret > 0 && vma_is_fsdax(vmas[0])) { > + ret = -EOPNOTSUPP; > + put_page(page[0]); > + } > up_read(&mm->mmap_sem); > } > >
Besides this patch series, are there other patches needed to make vma_is_fsdax() to work with device-dax? I applied this patch series on the libvdimm-for-next branch of nvdimm tree (ee95f4059a83), and found this patch series also failed device-dax mapping with vfio. It can be reproduced by following steps: 1. Attach PCI device at BDF 0000:03:10.2 to vfio-pci. # modprobe vfio-pci # lspci -n -s 0000:03:10.2 03:10.2 0200: 8086:1515 (rev 01) # echo 0000:03:10.2 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind # echo 8086:1515 > /sys/bus/pci/drivers/vfio-pci/new_id 2. Use RAM to emulate NVDIMM and create a device-dax device /dev/dax0.0 # cat /proc/iomem ... 100000000-2ffffffff : Persistent Memory (legacy) 100000000-2ffffffff : namespace0.0 ... # ndctl create-namespace -f -e namespace0.0 -m dax { "dev":"namespace0.0", "mode":"dax", "size":8453619712, "uuid":"e1db00bc-f830-4f1b-ac18-091ae7df4f93", "daxdevs":[ { "chardev":"dax0.0", "size":8453619712 } ] } 3. Create a VM with assigned PCI device in step 1 and the device-dax device in step 2. # qemu-system-x86_64 -machine pc,accel=kvm,nvdimm=on -smp host \ -m 4G,slots=32,maxmem=128G \ -drive file=VM_DISK_IMG.img,format=raw,if=virtio \ -object memory-backend-file,id=nv_be1,share=on,mem-path=/dev/dax0.0,size=4G,align=2M \ -device nvdimm,id=nv1,memdev=nv_be1 \ -device ioh3420,id=root.0,slot=4 \ -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:03:10.2,id=nic1,bus=pci.0,addr=0x6 It then fails with the following QEMU error messages: qemu-system-x86_64: -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:03:10.2,id=nic1,bus=pci.0,addr=0x6: VFIO_MAP_DMA: -95 qemu-system-x86_64: -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:03:10.2,id=nic1,bus=pci.0,addr=0x6: vfio_dma_map(0x5643804a92c0, 0x140000000, 0xffe00000, 0x7f2ed5200000) = -95 (Operation not supported) qemu-system-x86_64: -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:03:10.2,id=nic1,bus=pci.0,addr=0x6: vfio error: 0000:03:10.2: failed to setup container for group 52: memory listener initialization failed for container: Operation not supported I added the following debug messages after the get_user_pages_longterm() call in this patch, if (vmas[0] && vma_is_dax(vmas[0])) printk(KERN_DEBUG "%s: longterm failed for pfn 0x%lx, ret %d\n", __func__, page_to_pfn(page[0]), ret); and shows get_user_pages_longterm() returns -EOPNOTSUPP on the first device-dax page mapping. Haozhong _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm