On Wed, Dec 10, 2014 at 12:32:02AM +0100, Stefan Fritsch wrote: > Hi, > > in summer, I posted some paravirt patches for amd64. In response to the > comments I received then, I have created some infrastructure to binary > patch kernel code during boot. In order to get some feedback, I am posting > the whole paravirt & code patching diff here. Also, KVM users may be > interested in trying it (hi Antoine ;). > > For the codepatching part, the most interesting files are codepatch.c and > codepatch.h. In copy.S and cpu.c, I convert the code patching already > done for SMAP to the new infrastructure (if someone has a machine with > SMAP support, testing would be nice).
There aren't so many machines with SMAP commercially released only a handful of "2 in 1" devices with Core M processors. You should be able to test with the qemu support added by Intel however. ie qemu-system-x86_64 -cpu qemu64,+smap or qemu-system-x86_64 -cpu Broadwell > > The basic approach is to create macros that surround a to-be-patched code > part and store pointer, length, and a tag in a dedicated section. Then > there are functions to replace all code parts with a specific tag. Does > this part of the diff look sensible? What about i386? Though not included in your diff we can't assume the various multi byte nop sequences are valid there. The Intel instruction set reference says: "The multi-byte NOP instruction performs no operation on supported processors and generates undefined opcode exception on processors that do not support the multi-byte NOP instruction." It seems in practice they are supported on everything after 686/pentium pro? Though the code doing the patching could do a cpuid check.
