linux-kernel - Re: [RFC PATCH 5/6] kvm: Re-introduce memslots->nmemslots

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Message-ID: <20121206235848.GA30582@amt.cnet>
Date:	Thu, 6 Dec 2012 21:58:48 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	kvm@...r.kernel.org, gleb@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/6] kvm: Re-introduce memslots->nmemslots

On Wed, Dec 05, 2012 at 08:51:37PM -0700, Alex Williamson wrote:
> > > id_to_memslot seems like a good place to catch all the users since
> > > that's the only way to get a slot from a slot id after the array is
> > > sorted.  We need to check both is the slot in bounds (EINVAL), but also
> > > is it allocated (ENOENT).  id_to_memslot could both of these if we
> > > wanted to switch it to ERR_PTR.  Thanks,
> > > 
> > > Alex
> > 
> > There should never be a reference to a slot out of bounds by KVM itself
> > (BUG_ON). Only userspace can attempt a reference to such slot.
> 
> If I understand correctly, you're saying this last chunk is unique
> because kvm_get_dirty_log() is an internal interface and the test should
> be restricted to callers from userspace interfaces, namely
> kvm_vm_ioctl_get_dirty_log().  That sounds reasonable; book3s_pr seems
> to be the only caller that relies on kvm_get_dirty_log() validating the
> slot.  Thanks,
> 
> Alex

Yep - so you can move the check to such userspace interfaces, and bug on 
on WARN otherwise (in id_to_memslot).

Does that make sense??

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