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.williamson@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: Christoph Hellwig hch@lst.de Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Reported-by: Haozhong Zhang haozhong.zhang@intel.com Fixes: d475c6346a38 ("dax,ext2: replace XIP read and write with DAX I/O") Signed-off-by: Dan Williams dan.j.williams@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);@@ -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]);}
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