[vbox-dev] Mutual exclusion during read/modify/write

[Vilbig, Ric]

Hi,

I posted this on the OSE forum some weeks ago, but I did not get any response.  I hope someone on this list can give me some guidance, because this is getting critical for me.  Thanks.

I have a virtual device model plugged in through PDM, in which a PCIe switch is plugged into the ICH9 host bus, and a PCIe endpoint is connected to the secondary bus of the PCIe switch (each is a different PDM instance). The endpoint is capable of accessing system memory via DMA, which I model by calling PDMDevHlpPhysRead() and PDMDevHlpPhysWrite() from a separate thread that I have. So far so good.

Now I need to add support for PCIe "atomic" operations. These are a set of endpoint initiated read/modify/write operations that are carried out without interruption. It's quite easy to implement the read/modify/write part in my model, but I am concerned about the possibility of another VirtualBox thread doing another memory access in between the read/modify/write phases.

Is there a way to ensure nothing else can access memory during the critical steps of the read/modify/write? I have mutual exclusion between my own two threads, but I'm worried about guest software or other device models that are not in my control.

_____________________________________________

Ric Vilbig
Mentor Graphics, Emulation Division
46871 Bayside Parkway, Fremont CA, 94538
Phone:  510-354-7360
Mobile: 408-529-2365
email:  ric_vilbig at mentor.com<mailto:ric_vilbig at mentor.com>


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