Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934620Ab3FSJOb (ORCPT ); Wed, 19 Jun 2013 05:14:31 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:51990 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934311Ab3FSJJn (ORCPT ); Wed, 19 Jun 2013 05:09:43 -0400 From: Xiao Guangrong To: gleb@redhat.com Cc: avi.kivity@gmail.com, mtosatti@redhat.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Xiao Guangrong Subject: [PATCH 2/7] KVM: MMU: document clear_spte_count Date: Wed, 19 Jun 2013 17:09:20 +0800 Message-Id: <1371632965-20077-3-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1371632965-20077-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> References: <1371632965-20077-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061909-1618-0000-0000-0000041C936B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2508 Lines: 66 Document it to Documentation/virtual/kvm/mmu.txt Signed-off-by: Xiao Guangrong --- Documentation/virtual/kvm/mmu.txt | 4 ++++ arch/x86/include/asm/kvm_host.h | 5 +++++ arch/x86/kvm/mmu.c | 7 ++++--- 3 files changed, 13 insertions(+), 3 deletions(-) diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt index 869abcc..ce6df51 100644 --- a/Documentation/virtual/kvm/mmu.txt +++ b/Documentation/virtual/kvm/mmu.txt @@ -210,6 +210,10 @@ Shadow pages contain the following information: A bitmap indicating which sptes in spt point (directly or indirectly) at pages that may be unsynchronized. Used to quickly locate all unsychronized pages reachable from a given page. + clear_spte_count: + It is only used on 32bit host which helps us to detect whether updating the + 64bit spte is complete so that we can avoid reading the truncated value out + of mmu-lock. Reverse map =========== diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 966f265..1dac2c1 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -226,6 +226,11 @@ struct kvm_mmu_page { DECLARE_BITMAP(unsync_child_bitmap, 512); #ifdef CONFIG_X86_32 + /* + * Count after the page's spte has been cleared to avoid + * the truncated value is read out of mmu-lock. + * please see the comments in __get_spte_lockless(). + */ int clear_spte_count; #endif diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index c87b19d..77d516c 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -464,9 +464,10 @@ static u64 __update_clear_spte_slow(u64 *sptep, u64 spte) /* * The idea using the light way get the spte on x86_32 guest is from * gup_get_pte(arch/x86/mm/gup.c). - * The difference is we can not catch the spte tlb flush if we leave - * guest mode, so we emulate it by increase clear_spte_count when spte - * is cleared. + * The difference is we can not immediately catch the spte tlb since + * kvm may collapse tlb flush some times. Please see kvm_set_pte_rmapp. + * + * We emulate it by increase clear_spte_count when spte is cleared. */ static u64 __get_spte_lockless(u64 *sptep) { -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/