From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch] kvm: make cr3 loading more robust Date: Wed, 03 Jan 2007 14:00:07 +0200 Message-ID: <459B9AC7.6020506@qumranet.com> References: <20070103021057.GA11316@elte.hu> <459B695C.5090004@qumranet.com> <20070103115230.GB937@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel Return-path: To: Ingo Molnar In-Reply-To: <20070103115230.GB937-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Ingo Molnar wrote: > * Avi Kivity wrote: > > >>> rmap_write_protect() has a BUG_ON() if a physical address is not >>> found the the memslot. But this is a possible scenario if a buggy >>> guest OS loads an invalid or corrupted cr3 value. So exit more >>> gracefully. >>> >> I think a better solution is to detect the invalid cr3 in new_cr3(). >> That way the entire chain of error returns is avoided. >> > > i'm wondering what the right semantics would be though. Kill the VM > context? > > on a real CPU an invalid cr3 does nothing explicitly (besides being a > sure way to get a triple fault) - physical memory is always accessible, > non-present physical memory at most generates an #MCE, but is typically > just returning 0xff, right? So perhaps keep a non-mapped page filled > with 0xff and map non-existent RAM to that? But then this 'RAM' needs to > be made non-writable. That's a good solution. I don't see why it has to be made non-writable -- it has undefined content, and any old value will do. We have (or maybe had) something like that somewhere. > Looks a bit messy. Cleanest would be to kill the > VM context (without injecting any fault into the guest), but that would > then require an error return chain from set_cr3() ... > set_cr3() is fairly close to the top. I'm mostly worried about keeping the innards of the mmu clean. An alternative is to add a flag to the vcpu which would be examined on entry (vcpu->triple_faulted). -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV