Towards a configurable and slimmer x86 hypervisor

Transcription

1 Towards a configurable and slimmer x86 hypervisor Liu Wei Budapest July 11-13, 2017

2 Current state of affairs PV mode: no hardware extension needed, used in legacy systems, useful in certain cases like running unikernel and nested-virt without vvmx or vsvm HVM mode: needs hardware support and QEMU for emulation, has become the mainstream Xen VM mode PVH mode: essentially HVM without QEMU, under development Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 2 / 19

3 Two (big) projects Splitting PV and HVM code: Refactor x86 hypervisor code. Make guest supporting code configurable via Kconfig PV ABI in PVH container: Implement a PV ABI shim. Use it to translate PV hypercalls into PVH ones when necessary Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 3 / 19

4 Why splitting PV and HVM code? Users can pick and choose the guest interfaces Smaller binary, smaller attack surface Reclaim precious address space if PV is disabled, to let Xen support >16TB host memory more easily Improve x86 hypervisor code base *NOT* intending to kill PV in the hypervisor Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 4 / 19

5 Xen x86 PV memory layout Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 5 / 19

6 The conceptual map of code Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 6 / 19

7 The reality Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 7 / 19

8 Current code d o f o o (... ) { /... / i f (hvm) { do foo hvm ( ) ; return ; } / l o t s o f code to do foo f o r pv / } return ; Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 8 / 19

9 Current code d o b a r (... ) { /... / } i f (hvm) { / Some code / } ; i f ( pv ) { / Some code / } ; / l o t s o f code f o r common c a s e / i f (hvm) { / Some code / } ; i f ( pv ) { / Some code / } ; return ; Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 9 / 19

10 Future code do baz (... ) { / code f o r common c a s e / i f (hvm) do baz hvm ( ) ; i f ( pv ) do baz p v ( ) ; } return ; Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 10 / 19

11 Game plan for splitting PV and HVM code Identify all the components that need refactoring Dom0 builder Domain handling code Trap handling code Memory management code Guest memory accessor... Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 11 / 19

12 Game plan for splitting PV and HVM code Coarse-grained refactoring mostly for PV code Move code around Split code into manageable trunks Do some basic cleanups: Use better function names Use better coding style Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 12 / 19

13 Game plan for splitting PV and HVM code Fine-grained refactoring for both PV and HVM code Abstract out a set of guest interfaces Adjust internal interfaces between components if necessary Fix x86 common code Make PV and HVM configurable Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 13 / 19

14 Why PV ABI in PVH container? Continue to support PV in a more secure manner Have more than 128GB worth of 32bit PV guests Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 14 / 19

15 PV ABI in PVH container Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 15 / 19

16 Game plan for PV ABI in PVH container Build the PV shim essentially a stripped-down Xen hypervisor Go through all PV hypercall handlers, categorize them into the aforementeioned groups Further refactor PV guest supporting code: provide the real PV handlers and PV shim handlers while sharing as much code as possible Change the build system to pull in the right objects Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 16 / 19

17 Game plan for PV ABI in PVH container Adjust Xen toolstack Construct a PVH guest while using the PV shim as firmware Further improvements (open questions at the moment) Provide mechanism to parse guest kernel inside the container, something like pvgrub Provide mechanism to pass-through PCI devices (if that s still relevant) Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 17 / 19

18 Current status Doing coarse-grained refactoring: Dom0 builder (done) Domain handling code (done) Trap handling code (done) Memory management code (doing) Guest memory accessor... ETA: Some point in the future :) Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 18 / 19

19 Q&A Budapest July 11-13, 2017 Towards a configurable and slimmer x86 hypervisor 19 / 19