Re: [PATCH v2] core, x86: Add user return notifiers

Avi Kivity
2009-09-22T17:09:14Z

On 09/22/2009 06:50 PM, Avi Kivity wrote:
> On 09/22/2009 05:45 PM, Avi Kivity wrote:
>>> Would be nice to convert some existing open-coded return-to-user-space
>>> logic to this facility. One such candidate would be lockdep_sys_exit?
>>
>> I only implemented this for x86, while lockdep is arch independent.
>> If arch support is added, it should be trivial.
>>
>
> The lockdep_sys_exit bit is actually x86/s390 only, and can easily be
> adapted to use the new functionality on x86 only. I'll try it out.

Unfortunately it doesn't work out well. The notifier is called until
explicitly unregistered (since it relies on a bit in TIF_NOTIFY_MASK),
so we have to disarm it on the first return to usersspace or it spins
forever. We could re-arm it on the next kernel entry, but we don't have
a kernel entry notifier so we'll just be moving hooks from one point to
another.

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