From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 3/3] kvm mmu: alloc shadow pages with __GFP_ZERO Date: Wed, 18 Feb 2009 15:10:17 +0100 Message-ID: <20090218141017.GG8751@amd.com> References: <1234962540-7131-1-git-send-email-joerg.roedel@amd.com> <1234962540-7131-4-git-send-email-joerg.roedel@amd.com> <499C1158.7020401@redhat.com> <20090218135436.GF8751@amd.com> <499C1536.30302@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Marcelo Tosatti , kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Avi Kivity Return-path: Received: from wa4ehsobe005.messaging.microsoft.com ([216.32.181.15]:33718 "EHLO WA4EHSOBE006.bigfish.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751910AbZBROKp convert rfc822-to-8bit (ORCPT ); Wed, 18 Feb 2009 09:10:45 -0500 Content-Disposition: inline In-Reply-To: <499C1536.30302@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Feb 18, 2009 at 02:03:34PM +0000, Avi Kivity wrote: > Joerg Roedel wrote: > >The assertion which the attached patch removes fails sometimes. Remo= ving > >this assertion is the alternative solution to this problem ;-) > > > >From ca45f3a2e45cd7e76ca624bb1098329db8ff83ab Mon Sep 17 00:00:00 20= 01 > >From: Joerg Roedel > >Date: Wed, 18 Feb 2009 14:51:13 +0100 > >Subject: [PATCH] kvm mmu: remove assertion in kvm_mmu_alloc_page > > > >Signed-off-by: Joerg Roedel > >--- > > arch/x86/kvm/mmu.c | 1 - > > 1 files changed, 0 insertions(+), 1 deletions(-) > > > >diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > >index d93ecec..b226973 100644 > >--- a/arch/x86/kvm/mmu.c > >+++ b/arch/x86/kvm/mmu.c > >@@ -802,7 +802,6 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(s= truct kvm_vcpu *vcpu, > > set_page_private(virt_to_page(sp->spt), (unsigned long)sp); > > list_add(&sp->link, &vcpu->kvm->arch.active_mmu_pages); > > INIT_LIST_HEAD(&sp->oos_link); > >- ASSERT(is_empty_shadow_page(sp->spt)); > > bitmap_zero(sp->slot_bitmap, KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SL= OTS); > > sp->multimapped =3D 0; > > sp->parent_pte =3D parent_pte; > > =20 >=20 > sp->spt is allocated using mmu_memory_cache_alloc(), which zeros the = page. How can the assertion fail? In the code I see (current kvm-git) mmu_memory_cache_alloc() does zero nothing. It takes the page from the preallocated pool and returns it. The pool itself is filled with mmu_topup_memory_caches() which calls mmu_topup_memory_cache_page() to fill the mmu_page_cache (from which th= e sp->spt page is allocated later). And the mmu_topup_memory_cache_page() function calls alloc_page() and does not zero the result. This let the assertion trigger. Joerg --=20 | Advanced Micro Devices GmbH Operating | Karl-Hammerschmidt-Str. 34, 85609 Dornach bei M=C3=BCnchen System |=20 Research | Gesch=C3=A4ftsf=C3=BChrer: Jochen Polster, Thomas M. McCoy= , Giuliano Meroni Center | Sitz: Dornach, Gemeinde Aschheim, Landkreis M=C3=BCnchen | Registergericht M=C3=BCnchen, HRB Nr. 43632