Re: [PATCH] KVM: X86: Also reload the debug registers before kvm_x86->run() when the host is using them

[Paolo Bonzini]

On 09/07/21 12:05, Lai Jiangshan wrote:
> 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.
>
> It seems kvm_vcpu_check_breakpoint() handles only for code breakpoint
> and doesn't handle for data breakpoints.

Correct, there's a comment above the call.  But data breakpoint are much 
harder and relatively less useful.

> 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).

Good point, that should be fixed too.

Paolo