Thanks, sounds good! Of course the best solution would be in HVF itself,
similar to KVM and WHPX, but at least it's possible to work around it.
Paolo
Il mer 1 lug 2020, 20:37 Roman Bolshakov <r.bolsha...@yadro.com> ha scritto:
> On Tue, Jun 30, 2020 at 06:04:23PM +0200, Paolo Bonzini wrote:
> > On 30/06/20 17:50, Roman Bolshakov wrote:
> > > On Tue, Jun 30, 2020 at 02:33:42PM +0200, Paolo Bonzini wrote:
> > >> Can a signal interrupt hv_vcpu_run? If so you actually don't need
> > >> hv_vcpu_interrupt at all.
> > >
> > > Existing signal masking and SIG_IPI didn't work IIRC when I tried to
> add
> > > a primitive version of gdbstub support.
> >
> > You can try pthread_kill followed by hv_vcpu_interrupt if it doesn't.
> > The signal would be delivered after return to userspace.
> >
>
> I looked at the signal setup for HVF again. I was wrong with regards to
> SIG_IPI. It isn't delivered to vCPU because the signal is masked, this
> fixes it:
>
> diff --git a/target/i386/hvf/hvf.c b/target/i386/hvf/hvf.c
> index d81f569aed..7bf05bca21 100644
> --- a/target/i386/hvf/hvf.c
> +++ b/target/i386/hvf/hvf.c
> @@ -479,6 +479,7 @@ int hvf_init_vcpu(CPUState *cpu)
>
> pthread_sigmask(SIG_BLOCK, NULL, &set);
> sigdelset(&set, SIG_IPI);
> + pthread_sigmask(SIG_SETMASK, &set, NULL);
>
> init_emu();
> init_decoder();
>
> But the signal is delivered only after vmxexit, perhaps a sequence of
> pthread_kill() and hv_vcpu_interrupt() is really needed.
>
> So, there are two race windows on kernel-to-user border in v2: just
> before checking the deadline and vmenter and just after vmxexit and
> re-arm of preemption timer, that's two places where kicks could be lost.
> The approach you proposed seems to address them.
>
> Thanks,
> Roman
>
> > >> You can also require the preemption time, all
> > >> processor that support HVF have it, but never set it by default. The
> > >> deadline can be left at 0 all the time; instead, you toggle the bit in
> > >> the pin-based controls. In the signal handler you do:
> > >>
> > >> if (atomic_xchg(&env->hvf_in_guest, false)) {
> > >> wvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS,
> > >> rvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS)
> > >> | VMCS_PIN_BASED_CTLS_VMX_PREEMPT_TIMER);
> > >> }
> > >>
> > >> In the main loop you do:
> > >>
> > >> atomic_set(&env->hvf_guest_mode, true);
> > >> smp_mb();
> > >> hv_vcpu_run(...);
> > >> atomic_set(&env->hvf_guest_mode, false);
> > >>
> > >> and in the preemption timer vmexit handler:
> > >>
> > >> wvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS,
> > >> rvmcs(cpu->hvf_fd, VMCS_PIN_BASED_CTLS)
> > >> & ~VMCS_PIN_BASED_CTLS_VMX_PREEMPT_TIMER);
> > >>
> > >
>
>
