From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: [PATCH] prepopulate guest pages after write-protecting Date: Fri, 4 Apr 2008 14:56:44 -0300 Message-ID: <20080404175644.GA444@dmt> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Zdenek Kabelac , Avi Kivity Return-path: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces@lists.sourceforge.net Errors-To: kvm-devel-bounces@lists.sourceforge.net List-Id: kvm.vger.kernel.org Zdenek reported a bug where a looping "dmsetup status" eventually hangs on SMP guests. The problem is that kvm_mmu_get_page() prepopulates the shadow MMU before write protecting the guest page tables. By doing so, it leaves a window open where the guest can mark a pte as present while the host has shadow cached such pte as "notrap". Accesses to such address will fault in the guest without the host having a chance to fix the situation. Signed-off-by: Marcelo Tosatti Zdenek, can you confirm this fixes the problem? diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 5c4c166..c89bf23 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -852,9 +852,9 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, sp->gfn = gfn; sp->role = role; hlist_add_head(&sp->hash_link, bucket); - vcpu->arch.mmu.prefetch_page(vcpu, sp); if (!metaphysical) rmap_write_protect(vcpu->kvm, gfn); + vcpu->arch.mmu.prefetch_page(vcpu, sp); return sp; } ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace