[Lguest] [PATCH 3/25][V3] irq_flags / halt routines

[Glauber de Oliveira Costa]

On 8/15/07, Chris Wright <chrisw at sous-sol.org> wrote:
> * Glauber de Oliveira Costa (gcosta at redhat.com) wrote:
> > Only caveat, is that it has to be done before smp gets in the game, and
> > with interrupts disabled. (which makes the function in vsmp.c not eligible).
> >
> > My current option is to force VSMP to use PARAVIRT, as said before, and
> > then fill paravirt_arch_setup, which is currently unused, with code to
> > replace the needed paravirt_ops.fn.
> >
> > I don't know if there is any method to dynamically determine (at this
> > point) that we are in a vsmp arch, and if there are not, it will have to
> > get ifdefs anyway. But at least, they are far more local.
>
> between __cacheline_aligned_in_smp and other compile time bits based on
> VSMP specific INTERNODE_CACHE, etc. I think compile time the way to go.
>
> > I am okay with both, but after all the explanation, I don't think that
> > adding a new pvops is a bad idea. It would make things less cumbersome
> > in this case. Also, hacks like this save_fl may require changes to the
> > hypervisor, right? I don't even know where such hypervisor is, and how
> > easy it is to replace it (it may be deeply hidden in firmware)
>
> No hypervisor change needed.  Just the pv backend needs to return 0 or
> X86_EFLAGS_IF for save_flags (and similar translation on restore_flags).
> Xen uses a simple shared memory flag and does something which you could
> roughly translate into this:
>
>         xen_save_flags()
>         if (xen_vcpu_interrupts_enabled)
>                 return X86_EFLAGS_IF;
>         else
>                 return 0;
>
> This doesn't require any hypervisor changes.  Similarly, VSMP could do
> something along the lines of:
>
>         vsmp_save_flags()
>         flags = native_save_flags();
>         if (flags & X86_EFLAGS_IF) || (flags & X86_EFLAGS_AC)
>                 return X86_EFLAGS_IF;
>         else
>                 return 0;
>

I'm attaching to this message my idea on how would it work.
This is just for comments/considerations. If you all ack this, I'll
spread the changes over the patch series as needed, and then resend
the patches.

-- 
Glauber de Oliveira Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."
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