Re: [Xen-devel] [PATCH V2 0/6] mini-os: check and fix up against nested events in x86-64 kernel entry

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Ian Campbell, le Wed 17 Apr 2013 16:14:51 +0100, a écrit :
> On Thu, 2013-04-11 at 05:46 +0100, Xu Zhang wrote:
> > mini-os almost always use direct iret to return from interrupt.
> > But this operation is not atomic because Xen uses event mask to
> > enable/disable event delivery. So there is a window for nested 
> > events to happen after re-enabling event delivery and before
> > a direct iret.
> > 
> > The issues come with such non-atomicity have been discussed in:
> > http://lists.xen.org/archives/html/xen-devel/2007-06/msg00142.html
> > 
> > And also on Xen-devel:
> > http://markmail.org/message/jkzhzy6fyes6igcf
> > 
> > This patch checks and fixes up against nested events in a similar 
> > fashion of Linux 32bit pvops.
> > It checks against re-entrant of critical section in event handling 
> > callback. Try to fix up by coalescing the two stack frames into
> > one when the a nested event came. 
> > It then resumes execution as if the second event never happened.
> > 
> > It also refactors mini-os's x86-64 kernel entry assembly code.
> 
> Samuel are you now happy with this?

Yes.

> WRT making a case for a freeze exception it seems like this is fixing a
> pretty obvious bug in x86_64 mini-os event handling?

Yes.

Samuel

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