iommu=pt内核参数解析

PassthroughConfigname: CONFIG_IOMMU_DEFAULT_PASSTHROUGH default domain type
L->Passthrough
In linux kernel since version 3.10 (release Date:2013-06-30)
Trusted devices are identity-mapped, giving them unrestricted accessto memory with minimal performance overhead. Equivalent to passing"iommu.passthrough=1" (historically “iommu=pt”) on the command line.
If this mode is not supported by the lOMMU driver, the effectiveruntime default will fall back tO IOMMU DEFAULT DMA STRICT

./drivers/iommu/Kconfig:140:	  "iommu.passthrough=1" (historically "iommu=pt") on the command line.
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iommu=pt和iommu.passthrough=1是一样的。

linux对iommu=pt内核命令行参数解析的流程

arch/x86/kernel/pci-dma.c:189:early_param(“iommu”, iommu_setup);

176                 if (!strncmp(p, "pt", 2))
177                         iommu_set_
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