On 09/07/21 05:09, Lai Jiangshan wrote:
I just noticed that emulation.c fails to emulate with DBn. Is there any problem around it?
Just what you said, it's not easy and the needs are limited. I implemented kvm_vcpu_check_breakpoint because I was interested in using hardware breakpoints from gdb, even with unrestricted_guest=0 and invalid guest state, but that's it.
Paolo
For code breakpoint, if the instruction didn't cause vm-exit, (for example, the 2nd instruction when kvm emulates instructions back to back) emulation.c fails to emulate with DBn. For code breakpoint, if the instruction just caused vm-exit. It is difficult to analyze this case due to the complex priorities between vectored events and fault-like vm-exit. Anyway, if it is an instruction that vm-exit has priority over #DB, emulation.c fails to emulate with DBn. For data breakpoint, a #DB must be delivered to guest or to VMM (when guest-debug) after the instruction. But emulation.c doesn't do so. And the existence of both of effective DBn (guest debug) and guest DBn complicates the problem when we try to emulate them.
