9e6f3be806
This patch updates seL4 from the experimental branch of one year ago to the master branch of version 2.1. The transition has the following implications. In contrast to the experimental branch, the master branch has no way to manually define the allocation of kernel objects within untyped memory ranges. Instead, the kernel maintains a built-in allocation policy. This policy rules out the deallocation of once-used parts of untyped memory. The only way to reuse memory is to revoke the entire untyped memory range. Consequently, we cannot share a large untyped memory range for kernel objects of different protection domains. In order to reuse memory at a reasonably fine granularity, we need to split the initial untyped memory ranges into small chunks that can be individually revoked. Those chunks are called "untyped pages". An untyped page is a 4 KiB untyped memory region. The bootstrapping of core has to employ a two-stage allocation approach now. For creating the initial kernel objects for core, which remain static during the entire lifetime of the system, kernel objects are created directly out of the initial untyped memory regions as reported by the kernel. The so-called "initial untyped pool" keeps track of the consumption of those untyped memory ranges by mimicking the kernel's internal allocation policy. Kernel objects created this way can be of any size. For example the phys CNode, which is used to store page-frame capabilities is 16 MiB in size. Also, core's CSpace uses a relatively large CNode. After the initial setup phase, all remaining untyped memory is turned into untyped pages. From this point on, new created kernel objects cannot exceed 4 KiB in size because one kernel object cannot span multiple untyped memory regions. The capability selectors for untyped pages are organized similarly to those of page-frame capabilities. There is a new 2nd-level CNode (UNTYPED_CORE_CNODE) that is dimensioned according to the maximum amount of physical memory (1M entries, each entry representing 4 KiB). The CNode is organized such that an index into the CNode directly corresponds to the physical frame number of the underlying memory. This way, we can easily determine a untyped page selector for any physical addresses, i.e., for revoking the kernel objects allocated at a specific physical page. The downside is the need for another 16 MiB chunk of meta data. Also, we need to keep in mind that this approach won't scale to 64-bit systems. We will eventually need to replace the PHYS_CORE_CNODE and UNTYPED_CORE_CNODE by CNode hierarchies to model a sparsely populated CNode. The size constrain of kernel objects has the immediate implication that the VM CSpaces of protection domains must be organized via several levels of CNodes. I.e., as the top-level CNode of core has a size of 2^12, the remaining 20 PD-specific CSpace address bits are organized as a 2nd-level 2^4 padding CNode, a 3rd-level 2^8 CNode, and several 4th-level 2^8 leaf CNodes. The latter contain the actual selectors for the page tables and page-table entries of the respective PD. As another slight difference from the experimental branch, the master branch requires the explicit assignment of page directories to an ASID pool. Besides the adjustment to the new seL4 version, the patch introduces a dedicated type for capability selectors. Previously, we just used to represent them as unsigned integer values, which became increasingly confusing. The new type 'Cap_sel' is a PD-local capability selector. The type 'Cnode_index' is an index into a CNode (which is not generally not the entire CSpace of the PD). Fixes #1887 |
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README
=================================
Genode Operating System Framework
=================================
This is the source tree of the reference implementation of the Genode OS
architecture. For a general overview about the architecture, please refer to
the project's official website:
:Official project website for the Genode OS Framework:
[http://genode.org/documentation/general-overview]
The current implementation can be compiled for 8 different kernels: Linux,
L4ka::Pistachio, L4/Fiasco, OKL4, NOVA, Fiasco.OC, seL4, and a custom
kernel for running Genode directly on ARM-based hardware. Whereas the Linux
version serves us as development vehicle and enables us to rapidly develop the
generic parts of the system, the actual target platforms of the framework are
microkernels. There is no "perfect" microkernel - and neither should there be
one. If a microkernel pretended to be fit for all use cases, it wouldn't be
"micro". Hence, all microkernels differ in terms of their respective features,
complexity, and supported hardware architectures.
Genode allows the use of each of the kernels listed above with a rich set of
device drivers, protocol stacks, libraries, and applications in a uniform way.
For developers, the framework provides an easy way to target multiple different
kernels instead of tying the development to a particular kernel technology. For
kernel developers, Genode contributes advanced workloads, stress-testing their
kernel, and enabling a variety of application use cases that would not be
possible otherwise. For users and system integrators, it enables the choice of
the kernel that fits best with the requirements at hand for the particular
usage scenario.
Directory overview
##################
The source tree is composed of the following subdirectories:
:'doc':
This directory contains general documentation. Please consider the following
document for a quick guide to get started with the framework:
! doc/getting_started.txt
If you are curious about the ready-to-use components that come with the
framework, please review the components overview:
! doc/components.txt
:'repos':
This directory contains the so-called source-code repositories of Genode.
Please refer to the README file in the 'repos' directory to learn more
about the roles of the individual repositories.
:'tool':
Source-code management tools and scripts. Please refer to the README file
contained in the directory.
Contact
#######
The best way to get in touch with Genode developers and users is the project's
mailing list. Please feel welcome to join in!
:Genode Mailing Lists:
[http://genode.org/community/mailing-lists]