linux-kernel - Re: [PATCH v6 04/12] Add memory slot versioning and use it to provide fast guest write interface

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Date:	Thu, 07 Oct 2010 12:00:13 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...antech.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, kvm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v6 04/12] Add memory slot versioning and use it to provide
 fast guest write interface

  On 10/06/2010 10:08 PM, Gleb Natapov wrote:
> >  Malicious userspace can cause entry to be cached, ioctl
> >  SET_USER_MEMORY_REGION 2^32 times, generation number will match,
> >  mark_page_dirty_in_slot will be called with pointer to freed memory.
> >
> Hmm. To zap all cached entires on overflow we need to track them. If we
> will track then we can zap them on each slot update and drop "generation"
> entirely.

To track them you need locking.

Isn't SET_USER_MEMORY_REGION so slow that calling it 2^32 times isn't 
really feasible?

In any case, can use u64 generation count.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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