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Peter Anvin" , x86@kernel.org, Liran Alon , Nikita Leshenko , Barret Rhoden , Boris Ostrovsky , Matthew Wilcox , Konrad Rzeszutek Wilk Subject: [PATCH RFC 00/10] device-dax: Support devices without PFN metadata Date: Fri, 10 Jan 2020 19:03:03 +0000 Message-Id: <20200110190313.17144-1-joao.m.martins@oracle.com> X-Mailer: git-send-email 2.11.0 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9496 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2001100154 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9496 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2001100154 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey, Presented herewith a small series which allows device-dax to work without struct page to be used to back KVM guests memory. It's an RFC, and there's still some items we're looking at (see TODO below); but wondering if folks would be OK carving some time out of their busy schedules to provide feedback direction-wise on this work. In virtualized environments (specially those with no kernel-backed PV interfaces, and just SR-IOV), memory is largelly assigned to guests: either persistent with NVDIMMs or volatile for regular RAM. The kernel (hypervisor) tracks it with 'struct page' (64b) for each 4K page. Overall we're spending 16GB for each 1Tb of host memory tracked that the kernel won't need which could instead be used to create other guests. One of motivations of this series is to then get that memory used for 'struct page', when it is meant to solely be used by userspace. This is also useful for the case of memory backing guests virtual NVDIMMs. The other neat side effect is that the hypervisor has no virtual mapping of the guest and hence code gadgets (if found) are limited in their effectiveness. It is expected that a smaller (instead of total) amount of host memory is defined for the kernel (with mem=X or memmap=X!Y). For KVM userspace VMM (e.g. QEMU), the main thing that is needed is a device which open + mmap + close with a certain alignment (4K, 2M, 1G). That made us look at device-dax which does just that and so the work comprised here was improving what's there and the interfaces it uses. The series is divided as follows: * Patch 1 , 3: Preparatory work for patch 7 for adding support for vmf_insert_{pmd,pud} with dax pfn flags PFN_DEV|PFN_SPECIAL * Patch 2 , 4: Preparatory work for patch 7 for adding support for follow_pfn() to work with 2M/1G huge pages, which is what KVM uses for VM_PFNMAP. * Patch 5 - 7: One bugfix and device-dax support for PFN_DEV|PFN_SPECIAL, which encompasses mainly dealing with the lack of devmap, and creating a VM_PFNMAP vma. * Patch 8: PMEM support for no PFN metadata only for device-dax namespaces. At the very end of the cover letter (after scissors mark), there's a patch for ndctl to be able to create namespaces with '--mode devdax --map none'. * Patch 9: Let VFIO handle VM_PFNMAP without relying on vm_pgoff being a PFN. * Patch 10: The actual end consumer example for RAM case. The patch just adds a label storage area which consequently allows namespaces to be created. We picked PMEM legacy for starters. Thoughts, coments appreciated. Joao P.S. As an example to try this out: 1) add 'memmap=48G!16G' to the kernel command line, on a host with 64G, and kernel has 16G. 2) create a devdax namespace with 1G hugepages: $ ndctl create-namespace --verbose --mode devdax --map none --size 32G --align 1G -r 0 { "dev":"namespace0.0", "mode":"devdax", "map":"none", "size":"32.00 GiB (34.36 GB)", "uuid":"dfdd05cd-2611-46ac-8bcd-10b6194f32d4", "daxregion":{ "id":0, "size":"32.00 GiB (34.36 GB)", "align":1073741824, "devices":[ { "chardev":"dax0.0", "size":"32.00 GiB (34.36 GB)", "target_node":0, "mode":"devdax" } ] }, "align":1073741824 } 3) Add this to your qemu params: -m 32G -object memory-backend-file,id=mem,size=32G,mem-path=/dev/dax0.0,share=on,align=1G -numa node,memdev=mem TODO: * Discontiguous regions/namespaces: The work above is limited to max contiguous extent, coming from nvdimm dpa allocation heuristics -- which I take is because of what specs allow for persistent namespaces. But for volatile RAM case we would need handling of discontiguous extents (hence a region would represent more than a resource) to be less bound to how guests are placed on the system. I played around with multi-resource for device-dax, but I'm wondering about UABI: 1) whether nvdimm DPA allocation heuristics should be relaxed for RAM case (under certain nvdimm region bits); or if 2) device-dax would have it's own separate UABI to be used by daxctl (which would be also useful for hmem devices?). * MCE handling: For contiguous regions vm_pgoff could be set to the pfn in device-dax, which would allow collect_procs() to find the processes solely based on the PFN. But for discontiguous namespaces, not sure if this would work; perhaps looking at the dax-region pfn range for each DAX vma. * NUMA: For now excluded setting the target_node; while these two patches are being worked on[1][2]. [1] https://lore.kernel.org/lkml/157401276776.43284.12396353118982684546.stgit@dwillia2-desk3.amr.corp.intel.com/ [2] https://lore.kernel.org/lkml/157401277293.43284.3805106435228534675.stgit@dwillia2-desk3.amr.corp.intel.com/ Joao Martins (9): mm: Add pmd support for _PAGE_SPECIAL mm: Handle pmd entries in follow_pfn() mm: Add pud support for _PAGE_SPECIAL mm: Handle pud entries in follow_pfn() device-dax: Do not enforce MADV_DONTFORK on mmap() device-dax: Introduce pfn_flags helper device-dax: Add support for PFN_SPECIAL flags dax/pmem: Add device-dax support for PFN_MODE_NONE nvdimm/e820: add multiple namespaces support Nikita Leshenko (1): vfio/type1: Use follow_pfn for VM_FPNMAP VMAs arch/x86/include/asm/pgtable.h | 34 ++++- drivers/dax/bus.c | 3 +- drivers/dax/device.c | 78 ++++++++---- drivers/dax/pmem/core.c | 36 +++++- drivers/nvdimm/e820.c | 212 ++++++++++++++++++++++++++++---- drivers/vfio/vfio_iommu_type1.c | 6 +- mm/gup.c | 6 + mm/huge_memory.c | 15 ++- mm/memory.c | 67 ++++++++-- 9 files changed, 382 insertions(+), 75 deletions(-) 8>---------------- Subject: [PATCH] ndctl: add 'devdax' support for NDCTL_PFN_LOC_NONE diff --git a/ndctl/namespace.c b/ndctl/namespace.c index 7fb00078646b..2568943eb207 100644 --- a/ndctl/namespace.c +++ b/ndctl/namespace.c @@ -206,6 +206,8 @@ static int set_defaults(enum device_action mode) /* pass */; else if (strcmp(param.map, "dev") == 0) /* pass */; + else if (strcmp(param.map, "none") == 0) + /* pass */; else { error("invalid map location '%s'\n", param.map); rc = -EINVAL; @@ -755,9 +757,17 @@ static int validate_namespace_options(struct ndctl_region *region, if (param.map) { if (!strcmp(param.map, "mem")) p->loc = NDCTL_PFN_LOC_RAM; + else if (!strcmp(param.map, "none")) + p->loc = NDCTL_PFN_LOC_NONE; else p->loc = NDCTL_PFN_LOC_PMEM; + if (p->loc == NDCTL_PFN_LOC_NONE + && p->mode != NDCTL_NS_MODE_DAX) { + debug("--map=none only valid for devdax mode namespace\n"); + return -EINVAL; + } + if (ndns && p->mode != NDCTL_NS_MODE_MEMORY && p->mode != NDCTL_NS_MODE_DAX) { debug("%s: --map= only valid for fsdax mode namespace\n", -- 2.17.1