Re: [Xen-devel] [PATCH 4/6] mini-os/x86-64 entry: remove unnecessary event blocking

[Xu Zhang <xzhang@xxxxxxxxxx>]

Sorry about my delayed response. I just got some time to take a look and 
revise these patches.
It seems to me the bit of %gs manipulation is used for executing 
"do_hypervisor_callback" on a different stack. After it's done, it 
switches back to the original stack and resumes from there. The event 
mask is not touched during this process. I put mini-os under gdb just to 
verify, and for the runs I observed, event mask remains untouched.
Is there anything I am missing?

On 03/15/2013 03:16 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Mar 08, 2013 at 03:30:17PM -0600, Xu Zhang wrote:
> > We don't need to block events here because:
> >   - if we came from "hypervisor_callback", events are disabled at this point,
> >     no need to block again;
> Hm, I think I am not following it. It does a bit of %gs manipulation which
> looks to point to the cpu0_pda.irqcount.
>
> ?
> >   - if we came from "error_entry", we shouldn't touch event mask, for
> >     exception hanlding are meant to be interrupted by Xen events (virtual
> handling
> >     irq).
> >
> > Signed-off-by: Xu Zhang <xzhang@xxxxxxxxxx>
> > ---
> >   extras/mini-os/arch/x86/x86_64.S |    1 -
> >   1 files changed, 0 insertions(+), 1 deletions(-)
> >
> > diff --git a/extras/mini-os/arch/x86/x86_64.S b/extras/mini-os/arch/x86/x86_64.S
> > index 79e893f..5e0021b 100644
> > --- a/extras/mini-os/arch/x86/x86_64.S
> > +++ b/extras/mini-os/arch/x86/x86_64.S
> > @@ -185,7 +185,6 @@ ENTRY(hypervisor_callback2)
> >   
> >   error_exit:
> >         RESTORE_REST
> > -       XEN_BLOCK_EVENTS(%rsi)
> >   
> >   retint_kernel:
> >   retint_restore_args:
> > --
> > 1.7.7.6
> >
> >
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