On 05/09/2019 02:49, Masami Hiramatsu wrote: > On Wed, 4 Sep 2019 12:54:55 +0100 > Andrew Cooper <andrew.coop...@citrix.com> wrote: > >> On 04/09/2019 12:45, Masami Hiramatsu wrote: >>> Hi, >>> >>> These patches allow x86 instruction decoder to decode >>> xen-cpuid which has XEN_EMULATE_PREFIX, and prohibit >>> kprobes to probe on it. >>> >>> Josh reported that the objtool can not decode such special >>> prefixed instructions, and I found that we also have to >>> prohibit kprobes to probe on such instruction. >>> >>> This series can be applied on -tip master branch which >>> has merged Josh's objtool/perf sharing common x86 insn >>> decoder series. >> The paravirtualised xen-cpuid is were you'll see it most in a regular >> kernel, but be aware that it is also used for testing purposes in other >> circumstances, and there is an equivalent KVM prefix which is used for >> KVM testing. > Good catch! I didn't notice that. Is that really same sequance or KVM uses > another sequence of instructions for KVM prefix?
I don't know if you've spotted, but the prefix is a ud2a instruction followed by 'xen' in ascii. The KVM version was added in c/s 6c86eedc206dd1f9d37a2796faa8e6f2278215d2 > >> It might be better to generalise the decode support to "virtualisation >> escape prefix" or something slightly more generic. > Agreed, it is easy to expand it, we can switch the prefix template. > Could you tell me where I should look? I will add it. These are the only two I'm aware of. ~Andrew
