From patchwork Fri May 25 14:55:09 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eduardo Habkost X-Patchwork-Id: 161377 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 6CEDFB6FA4 for ; Sat, 26 May 2012 00:55:09 +1000 (EST) Received: from localhost ([::1]:35237 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SXvv1-0006ap-D6 for incoming@patchwork.ozlabs.org; Fri, 25 May 2012 10:55:07 -0400 Received: from eggs.gnu.org ([208.118.235.92]:35398) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SXvun-0006aR-DA for qemu-devel@nongnu.org; Fri, 25 May 2012 10:54:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SXvua-0002eB-AQ for qemu-devel@nongnu.org; Fri, 25 May 2012 10:54:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56414) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SXvua-0002dj-1y for qemu-devel@nongnu.org; Fri, 25 May 2012 10:54:40 -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 q4PEscPB013395 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 25 May 2012 10:54:38 -0400 Received: from blackpad.lan.raisama.net (ovpn-116-26.ams2.redhat.com [10.36.116.26]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q4PEsalZ019690; Fri, 25 May 2012 10:54:37 -0400 Received: by blackpad.lan.raisama.net (Postfix, from userid 500) id 9F6602005BA; Fri, 25 May 2012 11:55:09 -0300 (BRT) Date: Fri, 25 May 2012 11:55:09 -0300 From: Eduardo Habkost To: Marcelo Tosatti , Avi Kivity Message-ID: <20120525145509.GF8832@otherpad.lan.raisama.net> MIME-Version: 1.0 Content-Disposition: inline X-Fnord: you can see the fnord User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.25 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 209.132.183.28 Cc: Jan Kiszka , qemu-devel@nongnu.org, kvm@vger.kernel.org Subject: [Qemu-devel] [PATCH v4] uq/master: Expose CPUID leaf 7 only for -cpu host X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Changes v3 -> v4: - Wrap line at cpu_x86_fill_host() to make checkpatch.pl happy Changes v2 -> v3; - Check for kvm_enabled() before setting cpuid_7_0_ebx_features Changes v1 -> v2: - Use kvm_arch_get_supported_cpuid() instead of host_cpuid() on cpu_x86_fill_host(). We should use GET_SUPPORTED_CPUID for all bits on "-cpu host" eventually, but I am not changing all the other CPUID leaves because we may not be able to test such an intrusive change in time for 1.1. Description of the bug: Since QEMU 0.15, the CPUID information on CPUID[EAX=7,ECX=0] is being returned unfiltered to the guest, directly from the GET_SUPPORTED_CPUID return value. The problem is that this makes the resulting CPU feature flags unpredictable and dependent on the host CPU and kernel version. This breaks live-migration badly if migrating from a host CPU that supports some features on that CPUID leaf (running a recent kernel) to a kernel or host CPU that doesn't support it. Migration also is incorrect (the virtual CPU changes under the guest's feet) if you migrate in the opposite direction (from an old CPU/kernel to a new CPU/kernel), but with less serious consequences (guests normally query CPUID information only once on boot). Fortunately, the bug affects only users using cpudefs with level >= 7. The right behavior should be to explicitly enable those features on [cpudef] config sections or on the "-cpu" command-line arguments. Right now there is no predefined CPU model on QEMU that has those features: the latest Intel model we have is Sandy Bridge. I would like to get this fixed on 1.1, so I am submitting this patch, that enables those features only if "-cpu host" is being used (as we don't have any pre-defined CPU model that actually have those features). After 1.1 is released, we can make those features properly configurable on [cpudef] and -cpu configuration. One problem is: with this patch, users with the following setup: - Running QEMU 1.0; - Using a cpudef having level >= 7; - Running a kernel that supports the features on CPUID leaf 7; and - Running on a CPU that supports some features on CPUID leaf 7 won't be able to live-migrate to QEMU 1.1. But for these users live-migration is already broken (they can't live-migrate to hosts with older CPUs or older kernels, already), I don't see how to avoid this problem. Signed-off-by: Eduardo Habkost --- target-i386/cpu.c | 23 ++++++++++++++++------- target-i386/cpu.h | 2 ++ 2 files changed, 18 insertions(+), 7 deletions(-) diff --git a/target-i386/cpu.c b/target-i386/cpu.c index 65d9af6..2a1c24b 100644 --- a/target-i386/cpu.c +++ b/target-i386/cpu.c @@ -238,6 +238,8 @@ typedef struct x86_def_t { /* Store the results of Centaur's CPUID instructions */ uint32_t ext4_features; uint32_t xlevel2; + /* The feature bits on CPUID[EAX=7,ECX=0].EBX */ + uint32_t cpuid_7_0_ebx_features; } x86_def_t; #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE) @@ -521,6 +523,13 @@ static int cpu_x86_fill_host(x86_def_t *x86_cpu_def) x86_cpu_def->ext_features = ecx; x86_cpu_def->features = edx; + if (kvm_enabled() && x86_cpu_def->level >= 7) { + x86_cpu_def->cpuid_7_0_ebx_features = + kvm_arch_get_supported_cpuid(kvm_state, 0x7, 0, R_EBX); + } else { + x86_cpu_def->cpuid_7_0_ebx_features = 0; + } + host_cpuid(0x80000000, 0, &eax, &ebx, &ecx, &edx); x86_cpu_def->xlevel = eax; @@ -1185,6 +1194,7 @@ int cpu_x86_register(X86CPU *cpu, const char *cpu_model) env->cpuid_kvm_features = def->kvm_features; env->cpuid_svm_features = def->svm_features; env->cpuid_ext4_features = def->ext4_features; + env->cpuid_7_0_ebx = def->cpuid_7_0_ebx_features; env->cpuid_xlevel2 = def->xlevel2; object_property_set_int(OBJECT(cpu), (int64_t)def->tsc_khz * 1000, "tsc-frequency", &error); @@ -1451,13 +1461,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, *edx = 0; break; case 7: - if (kvm_enabled()) { - KVMState *s = env->kvm_state; - - *eax = kvm_arch_get_supported_cpuid(s, 0x7, count, R_EAX); - *ebx = kvm_arch_get_supported_cpuid(s, 0x7, count, R_EBX); - *ecx = kvm_arch_get_supported_cpuid(s, 0x7, count, R_ECX); - *edx = kvm_arch_get_supported_cpuid(s, 0x7, count, R_EDX); + /* Structured Extended Feature Flags Enumeration Leaf */ + if (count == 0) { + *eax = 0; /* Maximum ECX value for sub-leaves */ + *ebx = env->cpuid_7_0_ebx; /* Feature flags */ + *ecx = 0; /* Reserved */ + *edx = 0; /* Reserved */ } else { *eax = 0; *ebx = 0; diff --git a/target-i386/cpu.h b/target-i386/cpu.h index b5b9a50..2460f63 100644 --- a/target-i386/cpu.h +++ b/target-i386/cpu.h @@ -741,6 +741,8 @@ typedef struct CPUX86State { /* Store the results of Centaur's CPUID instructions */ uint32_t cpuid_xlevel2; uint32_t cpuid_ext4_features; + /* Flags from CPUID[EAX=7,ECX=0].EBX */ + uint32_t cpuid_7_0_ebx; /* MTRRs */ uint64_t mtrr_fixed[11];