Gregory, thanks for the reply; anyway, my question was about R3 context of the host. Since the host must emulate the E1000 behaviour, it doesn't need to access the I/O space on the host. So, why does it need to be in R0 context? Also, as far as I know, the file VBoxDD.so is a library for R3 context, and it has the references for functions running in R0 context (e.g. e1kRegWriteTDT). How can it be possible?
Kind Regards, Luca Carotenuto 2016-02-01 16:11 GMT+01:00 Gregory Woodbury <redwo...@gmail.com>: > Depending on the CPU architecture, Ring 3 processes cannot access the > I/O space without causing a General Protection Exception. > > Callback routines from IO requests are to let the application be told > that an operation is completed. > And thus have to be in the application's memory space, but they are > actually called from the > kernel in R0 space. There are special provisions in the x86 type > architecture for this, and > the callback routine has only a limited amount of freedom to access IO > space. > > In a fully emulated environment, this might not be necessary, but > using the hardware virtualization of KVM/QEMU, to access > the IO space still requires Ring0 privleges. I is a sort of > mind-bending set of restrictions and interactioins until one > gets used to thinking like the system developers did. > > > On Mon, Feb 1, 2016 at 6:59 AM, Luca Carotenuto > <luca.carotenuto...@gmail.com> wrote: > > > 1) As I understand, when we talk about Ring-0 context, we refer to kernel > > space, while Ring-3 context refers to user space. Am I right? > > > > 2) I'm looking inside the E1000 emulation code > > (/src/VBox/Devices/Network/DevE1000.cpp). > > Assuming that the above is right, for what concerns the registers > callbacks, > > I do not understand why those callbacks are compiled to be executed in > > Ring-0 context > > (When I use logging inside those functions, the thread name i R0). > > Infact, looking inside the VboxDD.so file in the "out/bin" directory > (using > > objdump tool), it seems that this code "belongs" to Ring-3 context, > > so why is it running in Ring-0 context? > > -- > G.Wolfe Woodbury > redwo...@gmail.com > -- Luca Carotenuto -- Luca Carotenuto
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