Re: [PATCH v6 2/4] Add NVMM accelerator: x86 CPU support

[Reinoud Zandijk]

On Thu, Apr 01, 2021 at 10:35:40AM +0200, Paolo Bonzini wrote:
> On 31/03/21 22:07, Reinoud Zandijk wrote:
> > +void nvmm_vcpu_kick(CPUState *cpu);
> 
> Not defined anywhere.

Hmmm, indeed. I think its a leftover of the former patch. Good catch.

> > +{
> > +#if NVMM_USER_VERSION == 1
> > +    struct sigaction sigact;
> > +    sigset_t set;
> > +
> > +    /* Install the IPI handler. */
> > +    memset(&sigact, 0, sizeof(sigact));
> > +    sigact.sa_handler = nvmm_ipi_signal;
> > +    sigaction(SIG_IPI, &sigact, NULL);
> > +
> > +    /* Allow IPIs on the current thread. */
> > +    sigprocmask(SIG_BLOCK, NULL, &set);
> > +    sigdelset(&set, SIG_IPI);
> > +    pthread_sigmask(SIG_SETMASK, &set, NULL);
> > +#else
> > +    /*
> > +     * We use the nvmm_vcpu_stop() mechanism, and don't use signals.
> > +     * Nothing to do.
> > +     */
> > +#endif
> 
> Since nvmm_vcpu_stop is very similar to KVM's immediate_exit mechanism, I
> think you still need to have a dummy signal handler to kick the VM out of
> the run loop *if it is in the kernel*.  The signal handler however can just
> do nothing.

Are you worried the in-kernel thread will somehow get stuck or halt on exit of
Qemu and left as a zombie?

> Also, can you just drop support for NVMM_USER_VERSION == 1?

Now thats a good suggestion. We could add support for it in the pkgsrc
package. When 9.0 gets retired, we could then retire it there without the need
to patch Qemu again.

> > diff --git a/target/i386/nvmm/meson.build b/target/i386/nvmm/meson.build
> > new file mode 100644
> > index 0000000000..c154e78014
> > --- /dev/null
> > +++ b/target/i386/nvmm/meson.build
> > @@ -0,0 +1,4 @@
> > +i386_softmmu_ss.add(when: 'CONFIG_NVMM', if_true: files(
> > +  'nvmm-all.c',
> > +  'nvmm-accel-ops.c',
> > +))
> 
> The nvmm library should be added here.

I am not sure what you mean by that. You provided a patch for the meson.build
file, will that not suffice?

With regards,
Reinoud

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