Hi, On 31/01/2019 13:52, Zhen Lei wrote: > Currently, many peripherals are faster than before. For example, the top > speed of the older netcard is 10Gb/s, and now it's more than 25Gb/s. But > when iommu page-table mapping enabled, it's hard to reach the top speed > in strict mode, because of frequently map and unmap operations. In order > to keep abreast of the times, I think it's better to set non-strict as > default.
Most users won't be aware of this relaxation and will have their system vulnerable to e.g. thunderbolt hotplug. See for example 4.3 Deferred Invalidation in http://www.cs.technion.ac.il/users/wwwb/cgi-bin/tr-get.cgi/2018/MSC/MSC-2018-21.pdf Why not keep the policy to secure by default, as we do for iommu.passthrough? And maybe add something similar to CONFIG_IOMMU_DEFAULT_PASSTRHOUGH? It's easy enough for experts to pass a command-line argument or change the default config. Thanks, Jean > > Below it's our iperf performance data of 25Gb netcard: > strict mode: 18-20 Gb/s > non-strict mode: 23.5 Gb/s > > Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com> > --- > Documentation/admin-guide/kernel-parameters.txt | 4 ++-- > drivers/iommu/iommu.c | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > b/Documentation/admin-guide/kernel-parameters.txt > index b799bcf..667221f 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1779,13 +1779,13 @@ > > iommu.strict= [ARM64] Configure TLB invalidation behaviour > Format: { "0" | "1" } > - 0 - Lazy mode. > + 0 - Lazy mode (default). > Request that DMA unmap operations use deferred > invalidation of hardware TLBs, for increased > throughput at the cost of reduced device isolation. > Will fall back to strict mode if not supported by > the relevant IOMMU driver. > - 1 - Strict mode (default). > + 1 - Strict mode. > DMA unmap operations invalidate IOMMU hardware TLBs > synchronously. > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 3ed4db3..10e0b49 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -43,7 +43,7 @@ > #else > static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA; > #endif > -static bool iommu_dma_strict __read_mostly = true; > +static bool iommu_dma_strict __read_mostly; > > struct iommu_callback_data { > const struct iommu_ops *ops; > -- > 1.8.3 > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-ker...@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
