From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759473AbdJRJbw (ORCPT ); Wed, 18 Oct 2017 05:31:52 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:54207 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934226AbdJRJbq (ORCPT ); Wed, 18 Oct 2017 05:31:46 -0400 X-Google-Smtp-Source: AOwi7QBjvztmjBUx18+cD7IGj7Zymz3aNIiKJMRBlQh8mxdegTPtlfGHnOZU/S38P2WV4j8aetmdfw== Subject: Re: [Part2 PATCH v5 31/31] KVM: X86: Restart the guest when insn_len is zero and SEV is enabled From: Paolo Bonzini To: Brijesh Singh , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Joerg Roedel , Borislav Petkov , Tom Lendacky References: <20171004131704.13266-1-brijesh.singh@amd.com> <20171004131704.13266-2-brijesh.singh@amd.com> Message-ID: <1ed3d49b-5373-fd4c-bf81-32dc6e3206cb@redhat.com> Date: Wed, 18 Oct 2017 11:31:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/10/2017 11:26, Paolo Bonzini wrote: > On 04/10/2017 15:17, Brijesh Singh wrote: >> + /* >> + * On AMD platforms, under certain conditions insn_len may be zero on #NPF. >> + * This can happen if a guest gets a page-fault on data access but the HW >> + * table walker is not able to read the instruction page (e.g instruction >> + * 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. >> + */ >> + if (unlikely(!insn_len) && >> + kvm_x86_ops->mem_enc_enabled && >> + kvm_x86_ops->mem_enc_enabled(vcpu)) >> + return 1; >> + > > Is it needed to test mem_enc_enabled? Could it instead test for the > availability of decode assists? More precisely, you could test "unlikely(insn && !insn_len)" here and, in svm.c, pass insn as static_cpu_has(X86_FEATURE_DECODEASSISTS) ? svm->vmcb->control.insn_bytes : 0 Paolo