On 2021/7/9 17:49, Paolo Bonzini wrote:
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.
Hello Paolo
I just remembered I once came across the patch, but I forgot it when
I wrote the mail.
It seems kvm_vcpu_check_breakpoint() handles only for code breakpoint
and doesn't handle for data breakpoints.
And no code handles DR7_GD bit when the emulation is not resulted from
vm-exit. (for example, the non-first instruction when kvm emulates
instructions back to back and the instruction accesses to DBn).
Thanks
Lai
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.
