From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751839Ab2DPDZT (ORCPT ); Sun, 15 Apr 2012 23:25:19 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:56881 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751166Ab2DPDZR (ORCPT ); Sun, 15 Apr 2012 23:25:17 -0400 Message-ID: <4F8B9115.2030807@linux.vnet.ibm.com> Date: Mon, 16 Apr 2012 11:25:09 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1 MIME-Version: 1.0 To: Avi Kivity CC: Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable References: <4F87FA69.5060106@linux.vnet.ibm.com> <4F87FC82.2050302@linux.vnet.ibm.com> <4F8AE64F.7080909@redhat.com> In-Reply-To: <4F8AE64F.7080909@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12041603-3864-0000-0000-000002470438 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/15/2012 11:16 PM, Avi Kivity wrote: > On 04/13/2012 01:14 PM, Xiao Guangrong wrote: >> Using bit 1 (PTE_LIST_WP_BIT) in rmap store the write-protect status >> to avoid unnecessary shadow page walking >> >> Signed-off-by: Xiao Guangrong >> --- >> arch/x86/kvm/mmu.c | 40 ++++++++++++++++++++++++++++++++++------ >> 1 files changed, 34 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 0c6e92d..8b71908 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -796,7 +796,9 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn) >> return level - 1; >> } >> >> -#define PTE_LIST_DESC (0x1ull) >> +#define PTE_LIST_DESC_BIT 0 >> +#define PTE_LIST_WP_BIT 1 >> +#define PTE_LIST_DESC (1 << PTE_LIST_DESC_BIT) >> #define PTE_LIST_FLAG_MASK (0x3ull) >> >> static void >> @@ -1067,6 +1069,12 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu) >> return mmu_memory_cache_free_objects(cache); >> } >> >> +static void host_page_write_protect(u64 *spte, unsigned long *rmapp) >> +{ >> + if (!(*spte & SPTE_HOST_WRITEABLE)) >> + __test_and_set_bit(PTE_LIST_WP_BIT, rmapp); >> +} >> > > Why is this needed, in addition to spte.SPTE_WRITE_PROTECT? > It is used to avoid the unnecessary overload for fast page fault if KSM is enabled. On the fast check path, it can see the gfn is write-protected by host, then the fast page fault path is not called.