DMA Remapping —— DMA请求类型

Remapping硬件把来自设备的DMA内存访问请求分成两种类型:

(1)Requests without address-space-identifier:这是来自endpoint device的正常的内存访问请求,包括访问类型(读,写,原子访问),DMA地址和大小,发起请求的设备标示;

(2)Requests with address-space-identifier:这种内存访问请求会包含额外的信息:表明支持virtual memoryendpoint devicetargeted process address space。除了常规请求信息外,还有process address space identifier (PASID),扩展属性:Execute-Requested (ER) flag
(to indicate reads that are instruction fetches)
Privileged-mode-Requested (PR) flag (to distinguish user versus supervisor access))等等。

参考资料:
Intel ® Virtualization Technology for Directed I/O

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