Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757971AbcC2Rop (ORCPT ); Tue, 29 Mar 2016 13:44:45 -0400 Received: from mga04.intel.com ([192.55.52.120]:8995 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753155AbcC2Rom (ORCPT ); Tue, 29 Mar 2016 13:44:42 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,412,1455004800"; d="scan'208";a="773999692" Subject: Re: [PATCH 1/4] KVM: MMU: fix permission_fault() To: Paolo Bonzini References: <1458911978-19430-1-git-send-email-guangrong.xiao@linux.intel.com> <56F54983.4010508@redhat.com> Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org From: Xiao Guangrong Message-ID: <56FABECE.40601@linux.intel.com> Date: Wed, 30 Mar 2016 01:43:42 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56F54983.4010508@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1749 Lines: 44 On 03/25/2016 10:21 PM, Paolo Bonzini wrote: > > > On 25/03/2016 14:19, Xiao Guangrong wrote: >> WARN_ON(pfec & (PFERR_PK_MASK | PFERR_RSVD_MASK)); >> - pfec |= PFERR_PRESENT_MASK; >> + errcode = PFERR_PRESENT_MASK; >> >> if (unlikely(mmu->pkru_mask)) { >> u32 pkru_bits, offset; >> @@ -193,11 +193,11 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, >> ((pte_access & PT_USER_MASK) << (PFERR_RSVD_BIT - PT_USER_SHIFT)); >> >> pkru_bits &= mmu->pkru_mask >> offset; >> - pfec |= -pkru_bits & PFERR_PK_MASK; >> + errcode |= -pkru_bits & PFERR_PK_MASK; >> fault |= (pkru_bits != 0); >> } >> >> - return -(uint32_t)fault & pfec; >> + return -(uint32_t)fault & errcode; >> } > > I have another doubt here. > > If you get a fault due to U=0, you would not get PFERR_PK_MASK. This > is checked implicitly through the pte_user bit which we moved to > PFERR_RSVD_BIT. However, if you get a fault due to W=0 _and_ > PKRU.AD=1 or PKRU.WD=1 for the page's protection key, would the PK > bit be set in the error code? If not, we would need something like > this: Based on the SDM: PK flag (bit 5). This flag is 1 if (1) IA32_EFER.LMA = CR4.PKE = 1; (2) the access causing the page-fault exception was a data access; (3) the linear address was a user-mode address with protection key i; and (5) the PKRU register (see Section 4.6.2) is such that either (a) ADi = 1; or (b) the following all hold: (i) WDi = 1; (ii) the access is a write access; and (iii) either CR0.WP = 1 or the access causing the page-fault exception was a user-mode access. So I think PKEY check and ordinary check are independent, i.e, PFEC.PKEY may be set even if the on permission on the page table is not adequate.