[vbox-dev] HGCM question...guest memory mapping
ramshankar.venkataraman at oracle.com
Wed Jul 11 22:31:47 PDT 2012
On 12/07/12 04:47, Jaikumar G wrote:
> Hello folks,
> So from the documentation for HGCM -
> A request is constructed in the guest physical memory, which must be
> locked by the guest. The physical address is passed to the VMM device
> using a 32 bit out edx, eax instruction.
> Can someone elaborate as to where in the code I can find as to how the
> physical address is passed to the VMM device ? Also how is the guest
> physical memory mapped to be accessed by the host ?
The guest physical memory is allocated and locked down in the guest
using the guest additions. Take a look at
vbglPhysHeapChunkAlloc() which calls into IPRT's RTMemContAlloc() which
is implemented for each supported platform which actually does the
physical memory allocation and lock down, obviously this allocation is
kept below the _4G range for port IO.
See VBoxGuestLib/GenericRequest.cpp: VbglGRPerform() The 32-bit physical
address of the request is transferred using port IO of the VMM PCI
device. The port address is initialized by the vboxguest PCI driver
(take a look at callers of VBoxGuestInitDevExt() if interested).
On the host side this translates as port IO which gets handled in
Devices/VMMDev/VMMDEv.cpp:vmmdevRequestHandler(). The devices accces
memory via PDM, in this case PDMDevHlpPhysRead() reads the guest
physical memory. The guest memory is allocated and locked down on the
host and handled as RAM/ROM ranges with context based access handlers.
> I looked around in the HGCM files in the both
> Additions/common/VBoxGuest* and in Devices/VMMDev but I was just going
> around in circles.
Devices/VMMDev/ is the place to look to see how these requests are
handled on the host side.
> Any pointers would be really appreciated.
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