Messages in this thread | | | Subject | Re: [PATCH v3 0/6] add non-strict mode support for arm-smmu-v3 | From | Robin Murphy <> | Date | Tue, 24 Jul 2018 22:51:58 +0100 |
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On 2018-07-12 7:18 AM, Zhen Lei wrote: > v2 -> v3: > Add a bootup option "iommu_strict_mode" to make the manager can choose which > mode to be used. The first 5 patches have not changed. > + iommu_strict_mode= [arm-smmu-v3] > + 0 - strict mode (default) > + 1 - non-strict mode > > v1 -> v2: > Use the lowest bit of the io_pgtable_ops.unmap's iova parameter to pass the strict mode: > 0, IOMMU_STRICT; > 1, IOMMU_NON_STRICT; > Treat 0 as IOMMU_STRICT, so that the unmap operation can compatible with > other IOMMUs which still use strict mode. In other words, this patch series > will not impact other IOMMU drivers. I tried add a new quirk IO_PGTABLE_QUIRK_NON_STRICT > in io_pgtable_cfg.quirks, but it can not pass the strict mode of the domain from SMMUv3 > driver to io-pgtable module.
What exactly is the issue there? We don't have any problem with other quirks like NO_DMA, and as I said before, by the time we're allocating the io-pgtable in arm_smmu_domain_finalise() we already know everything there is to know about the domain.
> Add a new member domain_non_strict in struct iommu_dma_cookie, this member will only be > initialized when the related domain and IOMMU driver support non-strict mode. > > v1: > In common, a IOMMU unmap operation follow the below steps: > 1. remove the mapping in page table of the specified iova range > 2. execute tlbi command to invalid the mapping which is cached in TLB > 3. wait for the above tlbi operation to be finished > 4. free the IOVA resource > 5. free the physical memory resource > > This maybe a problem when unmap is very frequently, the combination of tlbi > and wait operation will consume a lot of time. A feasible method is put off > tlbi and iova-free operation, when accumulating to a certain number or > reaching a specified time, execute only one tlbi_all command to clean up > TLB, then free the backup IOVAs. Mark as non-strict mode. > > But it must be noted that, although the mapping has already been removed in > the page table, it maybe still exist in TLB. And the freed physical memory > may also be reused for others. So a attacker can persistent access to memory > based on the just freed IOVA, to obtain sensible data or corrupt memory. So > the VFIO should always choose the strict mode. > > Some may consider put off physical memory free also, that will still follow > strict mode. But for the map_sg cases, the memory allocation is not controlled > by IOMMU APIs, so it is not enforceable. > > Fortunately, Intel and AMD have already applied the non-strict mode, and put > queue_iova() operation into the common file dma-iommu.c., and my work is based > on it. The difference is that arm-smmu-v3 driver will call IOMMU common APIs to > unmap, but Intel and AMD IOMMU drivers are not. > > Below is the performance data of strict vs non-strict for NVMe device: > Randomly Read IOPS: 146K(strict) vs 573K(non-strict) > Randomly Write IOPS: 143K(strict) vs 513K(non-strict)
How does that compare to passthrough performance? One thing I'm not entirely clear about is what the realistic use-case for this is - even if invalidation were infinitely fast, enabling translation still typically has a fair impact on overall system performance in terms of latency, power, memory bandwidth, etc., so I can't help wonder what devices exist today for which performance is critical and robustness* is unimportant, yet have crippled addressing capabilities such that they can't just use passthrough.
Robin.
* I don't want to say "security" here, since I'm actually a lot less concerned about the theoretical malicious endpoint/wild write scenarios than the the much more straightforward malfunctioning device and/or buggy driver causing use-after-free style memory corruption. Also, I'm sick of the word "security"...
> > Zhen Lei (6): > iommu/arm-smmu-v3: fix the implementation of flush_iotlb_all hook > iommu/dma: add support for non-strict mode > iommu/amd: use default branch to deal with all non-supported > capabilities > iommu/io-pgtable-arm: add support for non-strict mode > iommu/arm-smmu-v3: add support for non-strict mode > iommu/arm-smmu-v3: add bootup option "iommu_strict_mode" > > Documentation/admin-guide/kernel-parameters.txt | 12 +++++++ > drivers/iommu/amd_iommu.c | 4 +-- > drivers/iommu/arm-smmu-v3.c | 42 +++++++++++++++++++++++-- > drivers/iommu/dma-iommu.c | 25 +++++++++++++++ > drivers/iommu/io-pgtable-arm.c | 23 ++++++++------ > include/linux/iommu.h | 7 +++++ > 6 files changed, 98 insertions(+), 15 deletions(-) >
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