From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: [PATCH v2 3/3] Reenter guest after instruction emulation failure if emulation was due to access to non-mmio address. Date: Thu, 8 Jul 2010 12:41:12 +0300 Message-ID: <20100708094112.GS4689@redhat.com> References: <1278523006-21645-1-git-send-email-gleb@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org To: avi@redhat.com, mtosatti@redhat.com Return-path: Received: from mx1.redhat.com ([209.132.183.28]:25758 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753785Ab0GHJlN (ORCPT ); Thu, 8 Jul 2010 05:41:13 -0400 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o689fD8O017460 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Thu, 8 Jul 2010 05:41:13 -0400 Content-Disposition: inline In-Reply-To: <1278523006-21645-1-git-send-email-gleb@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: When shadow pages are in use sometimes KVM try to emulate an instruction when it accesses a shadowed page. If emulation fails KVM un-shadows the page and reenter guest to allow vcpu to execute the instruction. If page is not in shadow page hash KVM assumes that this was attempt to do MMIO and reports emulation failure to userspace since there is no way to fix the situation. This logic has a race though. If two vcpus tries to write to the same shadowed page simultaneously both will enter emulator, but only one of them will find the page in shadow page hash since the one who founds it also removes it from there, so another cpu will report failure to userspace and will abort the guest. Fix this by checking (in addition to checking shadowed page hash) that page that caused the emulation belongs to valid memory slot. If it is then reenter the guest to allow vcpu to reexecute the instruction. Signed-off-by: Gleb Natapov diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7070b41..6ed3176 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3930,6 +3930,29 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu) return EMULATE_FAIL; } +static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva) +{ + gpa_t gpa; + + /* + * if emulation was due to access to shadowed page table + * and it failed try to unshadow page and re-entetr the + * guest to let CPU execute the instruction. + */ + if (kvm_mmu_unprotect_page_virt(vcpu, gva)) + return true; + + gpa = kvm_mmu_gva_to_gpa_system(vcpu, gva, NULL); + + if (gpa == UNMAPPED_GVA) + return true; /* let cpu generate fault */ + + if (!kvm_is_error_hva(gfn_to_hva(vcpu->kvm, gpa >> PAGE_SHIFT))) + return true; + + return false; +} + int emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2, u16 error_code, @@ -3998,7 +4021,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu, ++vcpu->stat.insn_emulation; if (r) { - if (kvm_mmu_unprotect_page_virt(vcpu, cr2)) + if (reexecute_instruction(vcpu, cr2)) return EMULATE_DONE; if (emulation_type & EMULTYPE_SKIP) return EMULATE_FAIL; @@ -4019,12 +4042,7 @@ restart: r = x86_emulate_insn(&vcpu->arch.emulate_ctxt, &emulate_ops); if (r) { /* emulation failed */ - /* - * if emulation was due to access to shadowed page table - * and it failed try to unshadow page and re-entetr the - * guest to let CPU execute the instruction. - */ - if (kvm_mmu_unprotect_page_virt(vcpu, cr2)) + if (reexecute_instruction(vcpu, cr2)) return EMULATE_DONE; return handle_emulation_failure(vcpu); -- Gleb.