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 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? The un-acked changes look to be
mostly cleanups and refactoring rather than substantive changes. The
very last patch has meat in it and is unacked.

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?

Ian.

> 
> Xu Zhang (6):
>   mini-os/x86-64 entry: code clean-ups; no functional changes
>   mini-os/x86-64 entry: define macros for registers partial save and
>     restore; no functional changes
>   mini-os/x86-64 entry: code refactoring; no functional changes
>   mini-os/x86-64 entry: remove unnecessary event blocking
>   mini-os/x86-64 entry: defer RESTORE_REST until return
>   mini-os/x86-64 entry: check against nested events and try to fix up
> 
>  extras/mini-os/arch/x86/x86_64.S |  245 
> ++++++++++++++++++++++++--------------
>  1 files changed, 156 insertions(+), 89 deletions(-)
> 
> ---
> Changed since v1:
>  * Drop the chunky lookup table; use Linux x86-32's fixup strategy instead,
>    as suggested by Jeremy Fitzhardinge;
>  * Reflect Samuel Thibault's comments.
> 



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