From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:34332) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gnE4E-0001xL-0w for qemu-devel@nongnu.org; Fri, 25 Jan 2019 21:51:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gnE4C-00046T-W3 for qemu-devel@nongnu.org; Fri, 25 Jan 2019 21:51:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58080) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gnE4C-000463-NU for qemu-devel@nongnu.org; Fri, 25 Jan 2019 21:51:32 -0500 Date: Sat, 26 Jan 2019 00:51:29 -0200 From: Eduardo Habkost Message-ID: <20190126025129.GN4136@habkost.net> References: <1548381283-16688-1-git-send-email-luwei.kang@intel.com> <20190124183909.GA4136@habkost.net> <82D7661F83C1A047AF7DC287873BF1E172CCDB7C@SHSMSX101.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <82D7661F83C1A047AF7DC287873BF1E172CCDB7C@SHSMSX101.ccr.corp.intel.com> Subject: Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Kang, Luwei" Cc: "qemu-devel@nongnu.org" , "pbonzini@redhat.com" , "rth@twiddle.net" On Fri, Jan 25, 2019 at 02:21:20AM +0000, Kang, Luwei wrote: > > > Intel Processor Trace required CPUID[0x14] but the cpuid level is 0xd > > > when create a kvm guest with e.g. "-cpu qemu64,+intel-pt". > > > > > > Signed-off-by: Luwei Kang > > > --- > > > target/i386/cpu.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c index > > > 2f54125..da477b3 100644 > > > --- a/target/i386/cpu.c > > > +++ b/target/i386/cpu.c > > > @@ -5023,6 +5023,13 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp) > > > x86_cpu_adjust_feat_level(cpu, FEAT_C000_0001_EDX); > > > x86_cpu_adjust_feat_level(cpu, FEAT_SVM); > > > x86_cpu_adjust_feat_level(cpu, FEAT_XSAVE); > > > + > > > + /* Intel Processor Trace requires CPUID[0x14] */ > > > + if ((env->features[FEAT_7_0_EBX] & CPUID_7_0_EBX_INTEL_PT) && > > > + kvm_enabled()) { > > > + x86_cpu_adjust_level(cpu, &cpu->env.cpuid_min_level, 0x14); > > > + } > > > > This will require a new machine-type compatibility flag to enable the new behavior, so we don't change CPUID data under the guest feet during live migration. > > Hi Eduardo, > Thanks for your reply. I have some question on your comments. > The cpuid level come from specific machine-type (e.g. qemu64, Skylake-Server) and they are all 0xd, but Intel PT required 0x14 so I extend the cpuid level. > I don't fully understand what is the "require a new machine-type compatibility flag" mean, I need to add a new flag in each machine-type? > I try to do live migration with "-cpu qemu64,+intel-pt" and "-cpu host" are all passed test. We didn't change the cpuid data during live migration just initialize the cpuid data when create a new vcpu. Please correct me if anything wrong. CPUID data is not sent as part of the migration stream (it is recreated on the migration destination), so if "-cpu qemu,+intel-pt" results in different CPUID data, migration between QEMU 4.0 and 3.1 will make CPUID level change during live migration. This is not a serious issue, but it might confuse software running on the guest. We can fix that doing this: target/i386/cpu.c: static Property x86_cpu_properties[] = { ... DEFINE_PROP_BOOL("x-intel-pt-auto-level", X86CPU, intel_pt_auto_level, true), .... } ... static void x86_cpu_expand_features(X86CPU *cpu, Error **errp) { ... /* Intel Processor Trace requires CPUID[0x14] */ if ((env->features[FEAT_7_0_EBX] & CPUID_7_0_EBX_INTEL_PT) && cpu->intel_pt_auto_level) { x86_cpu_adjust_level(cpu, &cpu->env.cpuid_min_level, 0x14); } ... } hw/i386/pc.c: GlobalProperty pc_compat_3_1[] = { ... { TYPE_X86_CPU, "x-intel-pt-auto-leevl", "off" }, }; > Thanks, > Luwei Kang > > > > > > + > > > /* SVM requires CPUID[0x8000000A] */ > > > if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) { > > > x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, > > > 0x8000000A); > > > -- > > > 1.8.3.1 > > > > > > > -- > > Eduardo -- Eduardo