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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sun, 2013-04-21 at 01:22 +0100, Samuel Thibault wrote:
> Ian Campbell, le Wed 17 Apr 2013 16:14:51 +0100, a Ãcrit :
> > 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.

Thanks. George also Acked on IRC wrt the freeze so applied.

Thanks Xu.

Ian.


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