Re: [RFP-V2 0/3] Make mmu_notifier_invalidate_range_start able to sleep.

[Robin Holt <holt@sgi.com>]

On Tue, Feb 02, 2010 at 01:59:43PM +0100, Andrea Arcangeli wrote:
> On Tue, Feb 02, 2010 at 03:09:47AM -0500, Christoph Hellwig wrote:
> > On Mon, Feb 01, 2010 at 10:01:45PM -0600, Robin Holt wrote:
> > > XPMEM would like to utilize mmu_notifiers to track page table entry
> > > changes of the segment and keep the attachment page table/tlb information
> > > consistent.
> > 
> > Given that SGI just pushes XPMEM direclty into the distributions instead
> > of adding it upstream I don't really see the relevance of these patches.
> 
> That will then prevent upstream modules to build against those
> kernels. Not an huge issue, for a distro that's an ok compromise. My
> real issue with mainline is that while XPMEM is ok to break and
> corrupt memory if people uses XPMEM on top of shared mappings (instead
> of anonymous ones) by making a two liner change to the userland app
> opening xpmem device, but when next mmu notifier user comes and ask
> for full scheduling across shared mapping too as it needs security and
> not-trusted user can open /dev/xpmem (or whatever that device is
> located), we'll have to undo this work and fix it the real way (with
> config option MMU_NOTIFIER_SLEEPABLE=y). But if distro have to support
> XPMEM in default kernels, this hack is better because it won't
> slowdown the locking even if it leaves holes and corrupts memory when
> XPMEM can be opened by luser. It really depends if the user having

Where is it leaving holes and corrupting memory?

Robin

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