Xen Interdomain Semaphore

Xen Interdomain Semaphore

[Timothy Hayes]

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Hi,

I'm working with some data that's been mapped into two virtual machine
address spaces (this is kernel module code). Right now if I try to
manipulate the data there are race conditions so naturally I need a
constraint like a mutex or a semaphore. I'm not 100% certain, but I'm
guessing the Linux kernel semaphore isn't going to work as expected since it
puts a process to sleep for a wait() call and wakes a process up for the
signal() call. The domain in question won't be the same domain that created
the process.

I'm wondering if there is an interdomain semaphore for Xen; maybe someone
has written one already? Maybe there are some "best practices" when it comes
to something like this. Any tips would be really appreciated.

Kind regards
Tim Hayes

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Re: Xen Interdomain Semaphore

[Keir Fraser]

On 09/03/2009 21:25, "Timothy Hayes" <hayesti@tcd.ie> wrote:

> I'm working with some data that's been mapped into two virtual machine address
> spaces (this is kernel module code). Right now if I try to manipulate the data
> there are race conditions so naturally I need a constraint like a mutex or a
> semaphore. I'm not 100% certain, but I'm guessing the Linux kernel semaphore
> isn't going to work as expected since it puts a process to sleep for a wait()
> call and wakes a process up for the signal() call. The domain in question
> won't be the same domain that created the process.
>  
> I'm wondering if there is an interdomain semaphore for Xen; maybe someone has
> written one already? Maybe there are some "best practices" when it comes to
> something like this. Any tips would be really appreciated.

If you already have shared memory between two domains, it would be easy to
implement a spinlock, right? If you want a sleeping semaphore then in
addition you need an inter-domain event channel. You can block on that and
the 'other end' can wake you by pinging you on it.

 -- Keir