From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [patch] kvm: make cr3 loading more robust Date: Wed, 3 Jan 2007 12:59:11 +0100 Message-ID: <20070103115911.GA2786@elte.hu> References: <20070103021057.GA11316@elte.hu> <459B695C.5090004@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel Return-path: To: Avi Kivity Content-Disposition: inline In-Reply-To: <459B695C.5090004-atKUWr5tajBWk0Htik3J/w@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 * Avi Kivity wrote: > >[ Avi: this patch needs kvm_mmu_get_page() NULL return to not be ignored > > by mmu_alloc_roots()/nonpaging_init_context()/paging_new_cr3()/etc. > > and passed further down - i assume you are working on those > > issues already, or should i fix those too? ] > > kvm_mmu_get_page() cannot return NULL (before this patch), as we > ensure there are free pages before entry to page_fault. hm, where do we ensure that? kvm_mmu_get_page() calls kvm_mmu_alloc_page(), which might return NULL: static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, u64 *parent_pte) { struct kvm_mmu_page *page; if (list_empty(&vcpu->free_pages)) return NULL; and i dont see where we ensure that ->free_pages is not empty. The relevant callchain would be kvm_vmx_return() -> handle_cr() -> set_cr3() -> paging_new_cr3() -> mmu_alloc_roots() -> kvm_mmu_get_page(). is there some accounting that makes a NULL pointer return impossible? The only one i can see is the direct quering of vcpu->free_pages or the querying of n_free_mmu_pages, but neither seems to be done in this codepath. (but i might have missed it) Ingo ------------------------------------------------------------------------- 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