From patchwork Wed Sep 19 16:36:52 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Avi Kivity X-Patchwork-Id: 1478521 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork1.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork1.kernel.org (Postfix) with ESMTP id 39E893FE79 for ; Wed, 19 Sep 2012 16:37:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753816Ab2ISQhP (ORCPT ); Wed, 19 Sep 2012 12:37:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32837 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752455Ab2ISQhL (ORCPT ); Wed, 19 Sep 2012 12:37:11 -0400 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q8JGb9rA018522 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 19 Sep 2012 12:37:09 -0400 Received: from s01.tlv.redhat.com (s01.tlv.redhat.com [10.35.255.8]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q8JGb0uq008535; Wed, 19 Sep 2012 12:37:08 -0400 From: Avi Kivity To: Marcelo Tosatti Cc: kvm@vger.kernel.org, Xiao Guangrong Subject: [PATCH v3 05/10] KVM: MMU: Optimize pte permission checks Date: Wed, 19 Sep 2012 19:36:52 +0300 Message-Id: <1348072617-23575-6-git-send-email-avi@redhat.com> In-Reply-To: <1348072617-23575-1-git-send-email-avi@redhat.com> References: <1348072617-23575-1-git-send-email-avi@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.25 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org walk_addr_generic() permission checks are a maze of branchy code, which is performed four times per lookup. It depends on the type of access, efer.nxe, cr0.wp, cr4.smep, and in the near future, cr4.smap. Optimize this away by precalculating all variants and storing them in a bitmap. The bitmap is recalculated when rarely-changing variables change (cr0, cr4) and is indexed by the often-changing variables (page fault error code, pte access permissions). The permission check is moved to the end of the loop, otherwise an SMEP fault could be reported as a false positive, when PDE.U=1 but PTE.U=0. Noted by Xiao Guangrong. The result is short, branch-free code. Reviewed-by: Xiao Guangrong Signed-off-by: Avi Kivity --- arch/x86/include/asm/kvm_host.h | 7 +++++++ arch/x86/kvm/mmu.c | 38 ++++++++++++++++++++++++++++++++++++++ arch/x86/kvm/mmu.h | 19 ++++++++----------- arch/x86/kvm/paging_tmpl.h | 22 ++++------------------ arch/x86/kvm/x86.c | 11 ++++------- 5 files changed, 61 insertions(+), 36 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 64adb61..3318bde 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -287,6 +287,13 @@ struct kvm_mmu { union kvm_mmu_page_role base_role; bool direct_map; + /* + * Bitmap; bit set = permission fault + * Byte index: page fault error code [4:1] + * Bit index: pte permissions in ACC_* format + */ + u8 permissions[16]; + u64 *pae_root; u64 *lm_root; u64 rsvd_bits_mask[2][4]; diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index f297a2c..9c61889 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3516,6 +3516,38 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, } } +static void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) +{ + unsigned bit, byte, pfec; + u8 map; + bool fault, x, w, u, wf, uf, ff, smep; + + smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP); + for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) { + pfec = byte << 1; + map = 0; + wf = pfec & PFERR_WRITE_MASK; + uf = pfec & PFERR_USER_MASK; + ff = pfec & PFERR_FETCH_MASK; + for (bit = 0; bit < 8; ++bit) { + x = bit & ACC_EXEC_MASK; + w = bit & ACC_WRITE_MASK; + u = bit & ACC_USER_MASK; + + /* Not really needed: !nx will cause pte.nx to fault */ + x |= !mmu->nx; + /* Allow supervisor writes if !cr0.wp */ + w |= !is_write_protection(vcpu) && !uf; + /* Disallow supervisor fetches of user code if cr4.smep */ + x &= !(smep && u && !uf); + + fault = (ff && !x) || (uf && !u) || (wf && !w); + map |= fault << bit; + } + mmu->permissions[byte] = map; + } +} + static int paging64_init_context_common(struct kvm_vcpu *vcpu, struct kvm_mmu *context, int level) @@ -3524,6 +3556,7 @@ static int paging64_init_context_common(struct kvm_vcpu *vcpu, context->root_level = level; reset_rsvds_bits_mask(vcpu, context); + update_permission_bitmask(vcpu, context); ASSERT(is_pae(vcpu)); context->new_cr3 = paging_new_cr3; @@ -3552,6 +3585,7 @@ static int paging32_init_context(struct kvm_vcpu *vcpu, context->root_level = PT32_ROOT_LEVEL; reset_rsvds_bits_mask(vcpu, context); + update_permission_bitmask(vcpu, context); context->new_cr3 = paging_new_cr3; context->page_fault = paging32_page_fault; @@ -3612,6 +3646,8 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu) context->gva_to_gpa = paging32_gva_to_gpa; } + update_permission_bitmask(vcpu, context); + return 0; } @@ -3687,6 +3723,8 @@ static int init_kvm_nested_mmu(struct kvm_vcpu *vcpu) g_context->gva_to_gpa = paging32_gva_to_gpa_nested; } + update_permission_bitmask(vcpu, g_context); + return 0; } diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 2832081..5846607 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -89,17 +89,14 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu) return kvm_read_cr0_bits(vcpu, X86_CR0_WP); } -static inline bool check_write_user_access(struct kvm_vcpu *vcpu, - bool write_fault, bool user_fault, - unsigned long pte) +/* + * Will a fault with a given page-fault error code (pfec) cause a permission + * fault with the given access (in ACC_* format)? + */ +static inline bool permission_fault(struct kvm_mmu *mmu, unsigned pte_access, + unsigned pfec) { - if (unlikely(write_fault && !is_writable_pte(pte) - && (user_fault || is_write_protection(vcpu)))) - return false; - - if (unlikely(user_fault && !(pte & PT_USER_MASK))) - return false; - - return true; + return (mmu->permissions[pfec >> 1] >> pte_access) & 1; } + #endif diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 35a05dd..8f6c59f 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -169,7 +169,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, pt_element_t pte; pt_element_t __user *uninitialized_var(ptep_user); gfn_t table_gfn; - unsigned index, pt_access, uninitialized_var(pte_access); + unsigned index, pt_access, pte_access; gpa_t pte_gpa; bool eperm, last_gpte; int offset; @@ -237,24 +237,9 @@ retry_walk: goto error; } - if (!check_write_user_access(vcpu, write_fault, user_fault, - pte)) - eperm = true; - -#if PTTYPE == 64 - if (unlikely(fetch_fault && (pte & PT64_NX_MASK))) - eperm = true; -#endif + pte_access = pt_access & gpte_access(vcpu, pte); last_gpte = FNAME(is_last_gpte)(walker, vcpu, mmu, pte); - if (last_gpte) { - pte_access = pt_access & gpte_access(vcpu, pte); - /* check if the kernel is fetching from user page */ - if (unlikely(pte_access & PT_USER_MASK) && - kvm_read_cr4_bits(vcpu, X86_CR4_SMEP)) - if (fetch_fault && !user_fault) - eperm = true; - } walker->ptes[walker->level - 1] = pte; @@ -284,10 +269,11 @@ retry_walk: break; } - pt_access &= gpte_access(vcpu, pte); + pt_access &= pte_access; --walker->level; } + eperm |= permission_fault(mmu, pte_access, access); if (unlikely(eperm)) { errcode |= PFERR_PRESENT_MASK; goto error; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c4d451e..db97dda 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3672,20 +3672,17 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva, gpa_t *gpa, struct x86_exception *exception, bool write) { - u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0; + u32 access = ((kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0) + | (write ? PFERR_WRITE_MASK : 0); - if (vcpu_match_mmio_gva(vcpu, gva) && - check_write_user_access(vcpu, write, access, - vcpu->arch.access)) { + if (vcpu_match_mmio_gva(vcpu, gva) + && !permission_fault(vcpu->arch.walk_mmu, vcpu->arch.access, access)) { *gpa = vcpu->arch.mmio_gfn << PAGE_SHIFT | (gva & (PAGE_SIZE - 1)); trace_vcpu_match_mmio(gva, *gpa, write, false); return 1; } - if (write) - access |= PFERR_WRITE_MASK; - *gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, gva, access, exception); if (*gpa == UNMAPPED_GVA)