From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 051EB6B004A for ; Thu, 7 Oct 2010 12:03:57 -0400 (EDT) Received: by bwz10 with SMTP id 10so6593bwz.14 for ; Thu, 07 Oct 2010 09:03:54 -0700 (PDT) Date: Thu, 7 Oct 2010 18:03:41 +0200 From: Gleb Natapov Subject: Re: [PATCH v6 04/12] Add memory slot versioning and use it to provide fast guest write interface Message-ID: <20101007160340.GD4120@minantech.com> References: <1286207794-16120-1-git-send-email-gleb@redhat.com> <1286207794-16120-5-git-send-email-gleb@redhat.com> <20101005165738.GA32750@amt.cnet> <20101006111417.GX11145@redhat.com> <20101006143847.GB31423@amt.cnet> <20101006200836.GC4120@minantech.com> <4CAD9A2D.7020009@redhat.com> <20101007154248.GA30949@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101007154248.GA30949@amt.cnet> Sender: owner-linux-mm@kvack.org To: Marcelo Tosatti Cc: Avi Kivity , Gleb Natapov , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mingo@elte.hu, a.p.zijlstra@chello.nl, tglx@linutronix.de, hpa@zytor.com, riel@redhat.com, cl@linux-foundation.org List-ID: On Thu, Oct 07, 2010 at 12:42:48PM -0300, Marcelo Tosatti wrote: > On Thu, Oct 07, 2010 at 12:00:13PM +0200, Avi Kivity wrote: > > 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? > > Assuming it takes 1ms, it would take 49 days. > We may fail ioctl when max value is reached. The question is how much slot changes can we expect from real guest during its lifetime. > > In any case, can use u64 generation count. > > Agree. Yes, 64 bit ought to be enough for anybody. -- Gleb. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org