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

[Jim Mattson]

On Fri, Jul 9, 2021 at 9:59 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 09/07/21 18:35, Jim Mattson wrote:
> >>>> 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.
> >
> > Data breakpoints are actually quite useful. I/O breakpoints not so much.
>
> Normally yes; much less for the specific case of debugging
> invalid-guest-state or other invocations of the emulator.

Agreed. But if they don't actually work in-guest (because the emulator
ignores them), then their normal usefulness is curtailed.