From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brijesh Singh Subject: [RFC Part2 PATCH v3 26/26] KVM: X86: Restart the guest when insn_len is zero and SEV is enabled Date: Mon, 24 Jul 2017 15:03:03 -0500 Message-ID: <20170724200303.12197-27-brijesh.singh@amd.com> References: <20170724200303.12197-1-brijesh.singh@amd.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Thomas Gleixner , Borislav Petkov , Joerg Roedel , "Michael S . Tsirkin" , Paolo Bonzini , =?UTF-8?q?=5C=22Radim=20Kr=C4=8Dm=C3=A1=C5=99=5C=22?= , Tom Lendacky , Brijesh Singh To: linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org Return-path: Received: from mail-by2nam01on0071.outbound.protection.outlook.com ([104.47.34.71]:28576 "EHLO NAM01-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754478AbdGXUJJ (ORCPT ); Mon, 24 Jul 2017 16:09:09 -0400 In-Reply-To: <20170724200303.12197-1-brijesh.singh@amd.com> Sender: kvm-owner@vger.kernel.org List-ID: On AMD platform, under certain conditions insn_len may be zero on #NPF. This can happen if guest gets a page-fault on data access, but HW table walker is not able to read the instruction page (e.g instuction page is not present in memory). Typically, when insn_len is zero, x86_emulate_instruction() walks the guest page table and fetches the instruction bytes from guest memory. When SEV is enabled, the guest memory is encrypted with guest-specific key hence hypervisor will not able to fetch the instruction bytes. In those cases we simply restart the guest. I have encountered this issue when running kernbench inside the guest. Signed-off-by: Brijesh Singh --- arch/x86/kvm/mmu.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index ccb70b8..be41ad0 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4850,6 +4850,23 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code, if (mmio_info_in_cache(vcpu, cr2, direct)) emulation_type = 0; emulate: + /* + * On AMD platform, under certain conditions insn_len may be zero on #NPF. + * This can happen if guest gets a page-fault on data access, but HW table + * walker is not able to read the instruction page (e.g instuction page + * is not present). + * + * Typically, when insn_len is zero, x86_emulate_instruction() walks the + * guest page table and fetches the instruction bytes. When SEV is active, + * the guest memory is encrypted with guest key hence we will not able to + * fetch the instruction bytes. In those cases we simply restart the guest. + */ + if (unlikely(!insn_len)) { + if (kvm_x86_ops->memory_encryption_enabled && + kvm_x86_ops->memory_encryption_enabled(vcpu)) + return 1; + } + er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len); switch (er) { -- 2.9.4