maven: missing .idea/modules.xml

I have multimodule maven project. I'm trying to open it in the IDEA 10
If I open pom.xml, then the project is reindexed and reimported every time I open it
If I open folder which contains pom.xml, when idea complains about missing module.xml:

Cannot convert project: /home/dobrokot/f3server/.idea/modules.xml: /home/dobrokot/f3server/.idea/modules

Sometimes modules.xml is generated automatically, but I can't figure out when it is generated.  Sometimes it is generates differently, so I  can't just put into SVN.
How it's supposed to properly open maven project in the IDEA? Should I open f3server/pom.xml, f3server or generated f3server/f3server.ipr  ?
What is .idea/modules.xml for? Why it is generated, and when?

Thanks!