Re: [RFC PATCH 1/1] server extension: PCIe requirements


Greg Favor
 

On Mon, Jun 14, 2021 at 5:23 PM Josh Scheid <jscheid@...> wrote:

I understand that IOPMP is not an IOMMU, but to the extent that it is a general "bus master memory protection" widget, it can be used by M-mode to ensure simple things, such as that S-mode-SW-controlled PCIe initiators can not access address regions not accessible by S-mode. 

Yes, most likely IOPMP can be used to do this.
 
For example, the platform spec could avoid mentioning the IOPMP proposal, but state that the platform is required to have a mechanism to allow M-mode SW to control (including prevent) PCIe initiator access to regions of system address space.  While remaining open to custom implementations, it's clear on the functional intent.

That would be appropriate.  And, for example, one much simpler implementation approach (than the IOPMP proposals) would be to replicate a CPU PMP block as an "IO PMP" in front of each I/O device or group of devices.

That would allow M-mode software to only have to deal with one PMP software programming model across all masters in the system.

Greg

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