From patchwork Wed Apr 21 12:28:32 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aaron Lewis X-Patchwork-Id: 12216075 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 922BEC43460 for ; Wed, 21 Apr 2021 12:28:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5ABA960233 for ; Wed, 21 Apr 2021 12:28:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239819AbhDUM3T (ORCPT ); Wed, 21 Apr 2021 08:29:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58680 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239784AbhDUM3N (ORCPT ); Wed, 21 Apr 2021 08:29:13 -0400 Received: from mail-pf1-x44a.google.com (mail-pf1-x44a.google.com [IPv6:2607:f8b0:4864:20::44a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 593DCC06174A for ; Wed, 21 Apr 2021 05:28:40 -0700 (PDT) Received: by mail-pf1-x44a.google.com with SMTP id a7-20020a62bd070000b029025434d5ead4so10102734pff.0 for ; Wed, 21 Apr 2021 05:28:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=hti6/C7S7vW6DIR+6O+Sa2M6tGrNZI+uifII3BY38yI=; b=cxsmCugqcjA3V9ytn6+rhLxHK5qhBVgFYmWzATlcRDwv0LD0m9Yu6NF41h1AUclASZ 4IH7Yc+p6kAPWpKp4OdLVputZGFU5oxLXsaK6/Rh2I5ItontxCqqOlkVjhoykPGhHdFy ekZhoRR773mG26R9QcGq/1YiCFto7/Nii9m0yiqa3DozzK8/SS6C1M/ycErDHSm0+4O3 sDoCoL9Gw4eYtBpTn2KU/K9Yib/obGTr86z0wuUmuPQo6cHTJ84xyWyHColK2T+yeIBz QeCpPvv4UCk/3egkO/5C/AU9h0GDLErBofyLk7LdgWljmrCYqq27SXEUTz6wzH9rGLHp kfNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=hti6/C7S7vW6DIR+6O+Sa2M6tGrNZI+uifII3BY38yI=; b=W3/Q621Qx0Bd+2mm2ZeXQ2bhha+1+MupzTNKwMWnMZQzQxOy1o5KGvGUkb2Sx/0aq7 NUUqJErHqGnTKykcvjBIy+0nTH1SxIe3tyChNDaX2048Xc3yvpvBQqOz0cV9VZjT9OfN momU+Oi8esfKwfbuWDC+ZRSTxYdSbuCMonV4xSDDLzcKzzcHESIuTMs8gCRs5jnZfAwM IzHf4N6pnL1+PHOiRv6qvXoFQs5JMjh+Ct8l5js1k8wfT3/x8ZMfUyyrvKaF0XV77B+k 7RwVcLRtuPr0QKAnmYjCXvFa89oFdMIpQrOyNGRtBKpRtX1cTK53SH5glP3GoElG6Nc1 DX4Q== X-Gm-Message-State: AOAM530F6nY4W7wq5cEtyILjnglWw2x/VaYxbISRUhfGuZPNm7tiANLF G14rkRcjeQ9x20sUMEiQfnXlNetie5lEQzw7 X-Google-Smtp-Source: ABdhPJyRoIYoZpdyl7BZPuUKSep7mTSH08UBbVmFjyjH6ikGybxlgYE6j8uWW76HyJ2kJaTZhjiyV9dmtX2JY7+P X-Received: from aaronlewis1.sea.corp.google.com ([2620:15c:100:202:218c:70d5:29b9:db76]) (user=aaronlewis job=sendgmr) by 2002:a17:90a:8d82:: with SMTP id d2mr10708592pjo.200.1619008119827; Wed, 21 Apr 2021 05:28:39 -0700 (PDT) Date: Wed, 21 Apr 2021 05:28:32 -0700 Message-Id: <20210421122833.3881993-1-aaronlewis@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.31.1.498.g6c1eba8ee3d-goog Subject: [PATCH v2 1/2] kvm: x86: Allow userspace to handle emulation errors From: Aaron Lewis To: david.edmondson@oracle.com, seanjc@google.com Cc: jmattson@google.com, kvm@vger.kernel.org, Aaron Lewis Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Add a fallback mechanism to the in-kernel instruction emulator that allows userspace the opportunity to process an instruction the emulator was unable to. When the in-kernel instruction emulator fails to process an instruction it will either inject a #UD into the guest or exit to userspace with exit reason KVM_INTERNAL_ERROR. This is because it does not know how to proceed in an appropriate manner. This feature lets userspace get involved to see if it can figure out a better path forward. Signed-off-by: Aaron Lewis --- Documentation/virt/kvm/api.rst | 19 ++++++++++++++++++ arch/x86/include/asm/kvm_host.h | 6 ++++++ arch/x86/kvm/x86.c | 35 +++++++++++++++++++++++++++++---- include/uapi/linux/kvm.h | 23 ++++++++++++++++++++++ tools/include/uapi/linux/kvm.h | 23 ++++++++++++++++++++++ 5 files changed, 102 insertions(+), 4 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 307f2fcf1b02..fe6c3f1cae7e 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6233,6 +6233,25 @@ KVM_RUN_BUS_LOCK flag is used to distinguish between them. This capability can be used to check / enable 2nd DAWR feature provided by POWER10 processor. +7.24 KVM_CAP_EXIT_ON_EMULATION_FAILURE +-------------------------------------- + +:Architectures: x86 +:Parameters: args[0] whether the feature should be enabled or not + +With this capability enabled, the in-kernel instruction emulator packs the exit +struct of KVM_INTERNAL_ERROR with the instruction length and instruction bytes +when an error occurs while emulating an instruction. This allows userspace to +then take a look at the instruction and see if it is able to handle it more +gracefully than the in-kernel emulator. + +When this capability is enabled use the emulation_failure struct instead of the +internal struct for the exit struct. They have the same layout, but the +emulation_failure struct matches the content better. + +It is noted that KVM still exits on certain types (skip) even if this capability +is not enabled, and KVM will never exit if VMware #GP emulation fails. + 8. Other capabilities. ====================== diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 3768819693e5..07235d08e976 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1049,6 +1049,12 @@ struct kvm_arch { bool exception_payload_enabled; bool bus_lock_detection_enabled; + /* + * If exit_on_emulation_error is set, and the in-kernel instruction + * emulator fails to emulate an instruction, allow userspace + * the opportunity to look at it. + */ + bool exit_on_emulation_error; /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */ u32 user_space_msr_mask; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index eca63625aee4..9cdfb7fbead5 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3771,6 +3771,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_X86_USER_SPACE_MSR: case KVM_CAP_X86_MSR_FILTER: case KVM_CAP_ENFORCE_PV_FEATURE_CPUID: + case KVM_CAP_EXIT_ON_EMULATION_FAILURE: r = 1; break; #ifdef CONFIG_KVM_XEN @@ -5357,6 +5358,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, kvm->arch.bus_lock_detection_enabled = true; r = 0; break; + case KVM_CAP_EXIT_ON_EMULATION_FAILURE: + kvm->arch.exit_on_emulation_error = cap->args[0]; + r = 0; + break; default: r = -EINVAL; break; @@ -7119,8 +7124,31 @@ void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip) } EXPORT_SYMBOL_GPL(kvm_inject_realmode_interrupt); +static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu) +{ + struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt; + u64 insn_size = ctxt->fetch.end - ctxt->fetch.data; + struct kvm_run *run = vcpu->run; + + + run->exit_reason = KVM_EXIT_INTERNAL_ERROR; + run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION; + run->emulation_failure.ndata = 0; + run->emulation_failure.flags = 0; + if (insn_size) { + run->emulation_failure.ndata = 3; + run->emulation_failure.flags |= + KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES; + run->emulation_failure.insn_size = insn_size; + memcpy(run->emulation_failure.insn_bytes, + ctxt->fetch.data, sizeof(ctxt->fetch.data)); + } +} + static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) { + struct kvm *kvm = vcpu->kvm; + ++vcpu->stat.insn_emulation_fail; trace_kvm_emulate_insn_failed(vcpu); @@ -7129,10 +7157,9 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) return 1; } - if (emulation_type & EMULTYPE_SKIP) { - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; - vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; - vcpu->run->internal.ndata = 0; + if (kvm->arch.exit_on_emulation_error || + (emulation_type & EMULTYPE_SKIP)) { + prepare_emulation_failure_exit(vcpu); return 0; } diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index f6afee209620..d7d109e6998f 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -279,6 +279,9 @@ struct kvm_xen_exit { /* Encounter unexpected vm-exit reason */ #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 +/* Flags that describe what fields in emulation_failure hold valid data */ +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) + /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ struct kvm_run { /* in */ @@ -382,6 +385,25 @@ struct kvm_run { __u32 ndata; __u64 data[16]; } internal; + /* + * KVM_INTERNAL_ERROR_EMULATION + * + * "struct emulation_failure" is an overlay of "struct internal" + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error + * sub-types, this struct is ABI! It also needs to be backwards + * compabile with "struct internal". Take special care that + * "ndata" is correct, that new fields are enumerated in "flags", + * and that each flag enumerates fields that are 64-bit aligned + * and sized (so that ndata+internal.data[] is valid/accurate). + */ + struct { + __u32 suberror; + __u32 ndata; + __u64 flags; + __u8 insn_size; + __u8 insn_bytes[15]; + } emulation_failure; /* KVM_EXIT_OSI */ struct { __u64 gprs[32]; @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_DIRTY_LOG_RING 192 #define KVM_CAP_X86_BUS_LOCK_EXIT 193 #define KVM_CAP_PPC_DAWR1 194 +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h index f6afee209620..d7d109e6998f 100644 --- a/tools/include/uapi/linux/kvm.h +++ b/tools/include/uapi/linux/kvm.h @@ -279,6 +279,9 @@ struct kvm_xen_exit { /* Encounter unexpected vm-exit reason */ #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 +/* Flags that describe what fields in emulation_failure hold valid data */ +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) + /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ struct kvm_run { /* in */ @@ -382,6 +385,25 @@ struct kvm_run { __u32 ndata; __u64 data[16]; } internal; + /* + * KVM_INTERNAL_ERROR_EMULATION + * + * "struct emulation_failure" is an overlay of "struct internal" + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error + * sub-types, this struct is ABI! It also needs to be backwards + * compabile with "struct internal". Take special care that + * "ndata" is correct, that new fields are enumerated in "flags", + * and that each flag enumerates fields that are 64-bit aligned + * and sized (so that ndata+internal.data[] is valid/accurate). + */ + struct { + __u32 suberror; + __u32 ndata; + __u64 flags; + __u8 insn_size; + __u8 insn_bytes[15]; + } emulation_failure; /* KVM_EXIT_OSI */ struct { __u64 gprs[32]; @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_DIRTY_LOG_RING 192 #define KVM_CAP_X86_BUS_LOCK_EXIT 193 #define KVM_CAP_PPC_DAWR1 194 +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 #ifdef KVM_CAP_IRQ_ROUTING