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 | Paolo Bonzini <> | Date | Fri, 9 Jul 2021 11:49:00 +0200 |
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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.
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