Messages in this thread | | | Subject | Re: [PATCH] KVM: X86: Also reload the debug registers before kvm_x86->run() when the host is using them | From | Lai Jiangshan <> | Date | Fri, 9 Jul 2021 18:05:25 +0800 |
| |
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.
| |