From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52999) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dNFGU-0000Fd-8j for qemu-devel@nongnu.org; Tue, 20 Jun 2017 05:16:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dNFGS-0007t9-4D for qemu-devel@nongnu.org; Tue, 20 Jun 2017 05:16:02 -0400 Received: from mail-pf0-x241.google.com ([2607:f8b0:400e:c00::241]:36553) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1dNFGR-0007se-UH for qemu-devel@nongnu.org; Tue, 20 Jun 2017 05:16:00 -0400 Received: by mail-pf0-x241.google.com with SMTP id y7so21600713pfd.3 for ; Tue, 20 Jun 2017 02:15:59 -0700 (PDT) From: guangrong.xiao@gmail.com Date: Tue, 20 Jun 2017 17:15:25 +0800 Message-Id: <20170620091526.4287-7-xiaoguangrong@tencent.com> In-Reply-To: <20170620091526.4287-1-xiaoguangrong@tencent.com> References: <20170620091526.4287-1-xiaoguangrong@tencent.com> Subject: [Qemu-devel] [PATCH v2 6/7] KVM: MMU: clarify fast_pf_fix_direct_spte List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: pbonzini@redhat.com, mtosatti@redhat.com, avi.kivity@gmail.com, rkrcmar@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Xiao Guangrong From: Xiao Guangrong The writable spte can not be locklessly fixed and add a WARN_ON() to trigger the warning if something out of our mind happens, that is good for us to track if the log for writable spte is missed on the fast path Signed-off-by: Xiao Guangrong --- arch/x86/kvm/mmu.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index c011ab0..7711953 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3240,6 +3240,15 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, WARN_ON(!sp->role.direct); /* + * the original spte can not be writable as only the spte which + * fulfills is_access_track_spte() or + * spte_can_locklessly_be_made_writable() can be locklessly fixed, + * for the former, the W bit is always cleared, for the latter, + * there is nothing to do if it is already writable. + */ + WARN_ON(is_writable_pte(old_spte)); + + /* * Theoretically we could also set dirty bit (and flush TLB) here in * order to eliminate unnecessary PML logging. See comments in * set_spte. But fast_page_fault is very unlikely to happen with PML @@ -3254,7 +3263,7 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, if (cmpxchg64(sptep, old_spte, new_spte) != old_spte) return false; - if (is_writable_pte(new_spte) && !is_writable_pte(old_spte)) { + if (is_writable_pte(new_spte)) { /* * The gfn of direct spte is stable since it is * calculated by sp->gfn. -- 2.9.4