From patchwork Fri Nov 15 08:35:00 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: pingfan liu X-Patchwork-Id: 291509 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from ozlabs.org (localhost [IPv6:::1]) by ozlabs.org (Postfix) with ESMTP id E4C272C041F for ; Fri, 15 Nov 2013 19:49:41 +1100 (EST) Received: from mail-ob0-x233.google.com (mail-ob0-x233.google.com [IPv6:2607:f8b0:4003:c01::233]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 8421A2C0335 for ; Fri, 15 Nov 2013 19:34:24 +1100 (EST) Received: by mail-ob0-f179.google.com with SMTP id wn1so3437818obc.24 for ; Fri, 15 Nov 2013 00:34:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id; bh=eNVAdl7Tyj5SEwMXzmcBymumdGBu1+gfYxsCYyDW79o=; b=Ip9sbFk97yLq9Zx9FvKfRkwsJIeMsPW0UQWsk+LITnf18vEKizTeph1/VXGISbMXr5 X7ySxz4l4QXpXOadGNY4W3KqsyIb3/8ZK9mnlVHkIMUmaze0FP18gpc/Oq7rC4jc+Wwa PzSwCTJjfFznVOvVZ7MMc1gm8LvUJz0RHazaRQ7kd6Vp2dPOGmaCCunk44I95dN624ip CNwftn5KoAL92697Wtg8vtI7Mn8+cW7Nrzv6HxwtnGSvqQYFlzHBpDmuh1o6Msy7yt27 UOcLBF538eIH0oZiUhLn3B0J9QsVrG5fFHF2rmNWl1rGtbNR7MhkRC1PAvwZM/MaahNs dDDw== X-Received: by 10.60.45.196 with SMTP id p4mr722258oem.81.1384504460405; Fri, 15 Nov 2013 00:34:20 -0800 (PST) Received: from localhost ([202.108.130.138]) by mx.google.com with ESMTPSA id ii8sm2753970obb.11.2013.11.15.00.34.18 for (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Fri, 15 Nov 2013 00:34:19 -0800 (PST) From: Liu Ping Fan To: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org Subject: [PATCH v4] powerpc: kvm: fix rare but potential deadlock scene Date: Fri, 15 Nov 2013 16:35:00 +0800 Message-Id: <1384504501-19348-1-git-send-email-pingfank@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 X-Mailman-Approved-At: Fri, 15 Nov 2013 19:49:16 +1100 Cc: Paul Mackerras , Alexander Graf X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.16rc2 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Since kvmppc_hv_find_lock_hpte() is called from both virtmode and realmode, so it can trigger the deadlock. Suppose the following scene: Two physical cpuM, cpuN, two VM instances A, B, each VM has a group of vcpus. If on cpuM, vcpu_A_1 holds bitlock X (HPTE_V_HVLOCK), then is switched out, and on cpuN, vcpu_A_2 try to lock X in realmode, then cpuN will be caught in realmode for a long time. What makes things even worse if the following happens, On cpuM, bitlockX is hold, on cpuN, Y is hold. vcpu_B_2 try to lock Y on cpuM in realmode vcpu_A_2 try to lock X on cpuN in realmode Oops! deadlock happens Signed-off-by: Liu Ping Fan Reviewed-by: Paul Mackerras --- v4: remove the over-engineered part and keep it simple, also add some notes. --- arch/powerpc/kvm/book3s_64_mmu_hv.c | 6 +++++- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 4 ++++ 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c index 842f081..abf81fe 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -473,11 +473,14 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr, slb_v = vcpu->kvm->arch.vrma_slb_v; } + preempt_disable(); /* Find the HPTE in the hash table */ index = kvmppc_hv_find_lock_hpte(kvm, eaddr, slb_v, HPTE_V_VALID | HPTE_V_ABSENT); - if (index < 0) + if (index < 0) { + preempt_enable(); return -ENOENT; + } hptep = (unsigned long *)(kvm->arch.hpt_virt + (index << 4)); v = hptep[0] & ~HPTE_V_HVLOCK; gr = kvm->arch.revmap[index].guest_rpte; @@ -485,6 +488,7 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr, /* Unlock the HPTE */ asm volatile("lwsync" : : : "memory"); hptep[0] = v; + preempt_enable(); gpte->eaddr = eaddr; gpte->vpage = ((v & HPTE_V_AVPN) << 4) | ((eaddr >> 12) & 0xfff); diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index 9c51544..ea17b30 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -749,6 +749,10 @@ static int slb_base_page_shift[4] = { 20, /* 1M, unsupported */ }; +/* When called from virtmode, this func should be protected by + * preempt_disable(), otherwise, the holding of HPTE_V_HVLOCK + * can trigger deadlock issue. + */ long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr, unsigned long slb_v, unsigned long valid) {