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From: Sasha Levin <levinsasha928@gmail.com>
To: Avi Kivity <avi@redhat.com>
Cc: kvm@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH v2 1/2] KVM: MMIO: Lock coalesced device when checking for available entry
Date: Mon, 18 Jul 2011 13:15:51 +0300	[thread overview]
Message-ID: <1310984151.8209.7.camel@lappy> (raw)
In-Reply-To: <4E2401E6.8020200@redhat.com>

On Mon, 2011-07-18 at 12:50 +0300, Avi Kivity wrote:
> On 07/18/2011 12:29 PM, Sasha Levin wrote:
> > >  Hmm.  This means we take the lock for every I/O, whether it hits
> > >  coalesced mmio or not.
> > >
> > >  We need to do the range check before taking the lock and the space check
> > >  after taking the lock.
> > >
> >
> > I'll fix that.
> >
> > Shouldn't the range check be also locked somehow? Currently it is
> > possible that a coalesced region was removed while we are checking the
> > ranges, and we won't issue a mmio exit as the host expects
> 
> It's "locked" using rcu.
> 

Where is that happening?

All the coalesced zones are stored under the coalesced "device" in a
simple array. When adding and removing zones, kvm->slots_lock is taken -
I don't see anything which prevents a range check during zone removal
unless slots_lock prevents IO.

-- 

Sasha.


  reply	other threads:[~2011-07-18 10:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-15 11:37 [PATCH v2 1/2] KVM: MMIO: Lock coalesced device when checking for available entry Sasha Levin
2011-07-15 11:37 ` [PATCH v2 2/2] x86: Raise the hard VCPU count limit Sasha Levin
2011-07-21  9:24   ` Ingo Molnar
2011-07-18  8:11 ` [PATCH v2 1/2] KVM: MMIO: Lock coalesced device when checking for available entry Avi Kivity
2011-07-18  9:29   ` Sasha Levin
2011-07-18  9:50     ` Avi Kivity
2011-07-18 10:15       ` Sasha Levin [this message]
2011-07-18 11:43         ` Avi Kivity
2011-07-18 12:03           ` Sasha Levin
2011-07-18 12:29             ` Avi Kivity
2011-07-18 12:58               ` Sasha Levin
2011-07-18 13:11                 ` Avi Kivity

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