On Wed, Nov 30, 2016 at 8:49 AM, PX seawolf.peng@gmail.com wrote:
I want to allocate a contiguous physical memory block (larger than a physical page) and map it to contiguous virtual addresses in the vspace, what's the best way to do it? Are there existing libraries allowing me to do that?
Not super familiar with the library sitch, but at a fundamental level:
- First you need an untyped of the correct size (and possibly at the correct position in physical memory), which may be available to you immediately, or you'll need to retype a larger one.
- Then you can retype it into page objects. A single seL4_UntypedRetype call can give you many pages, so you just need to choose the appropriate page size. If you wanted a 4MB contiguous block on x86_64, you could retype a 4MB untyped into two 2MB pages. If you wanted a 1MB contiguous block, you could retype a 1MB untyped into 256 4KB pages (as it happens, 256 is the default maximum number of objects you can make in an UntypedRetype call).
- Then you can seL4_$ARCH_{PageDirectory/Table/PDPT/etc}_Map and ultimately seL4_$ARCH_Page_Map them into contiguous virtual addresses.
(libsimple / vka / allocman are the things to look at in the seL4 userland stack, and there's a bit of this sort of stuff in the tutorial on the wiki.)
Thanks, Jeff