On 01/02/2019 15:58, Jan Beulich wrote: >>>> On 01.02.19 at 15:49, <andrew.coop...@citrix.com> wrote: >> c/s 9338a37d "x86/svm: implement debug events" added support for >> introspecting >> ICEBP debug exceptions, but didn't account for the fact that >> svm_get_insn_len() (previously __get_instruction_length) can fail and may >> already raise #GP for the guest. >> >> If svm_get_insn_len() fails, return back to guest context rather than >> continuing and mistaking a trap-style VMExit for a fault-style one. > My reading of the last part of this sentence is that the exit in > question is a trap-style one. Is my English failing me here?
Your reading of my sentence is correct, but I was confused when writing it. ICEBP is a fault-style intercept. However, when svm_get_insn_len() fails, it will inject #GP and return 0. This then gets passed into hvm_monitor_debug() or the #DB re-injected as-was. If it were just getting insn_len incorrectly as 0, then the guest would livelock as we wouldn't inject the #DB with trap semantics it requires, but as the #GP is already raised, this will combine to #DF. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
