Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Eduardo Habkost]

Hi,

Thanks for the patch.  Comment below:

On Thu, Jan 24, 2019 at 08:54:43PM -0500, Luwei Kang 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 <luwei.kang@intel.com>
> ---
>  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.

> +
>          /* 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

[Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Luwei Kang]

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 <luwei.kang@intel.com>
---
 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);
+        }
+
         /* 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

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Kang, Luwei]

> > 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 <luwei.kang@intel.com>
> > ---
> >  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.

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

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Eduardo Habkost]

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 <luwei.kang@intel.com>
> > > ---
> > >  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

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Kang, Luwei]

> > > > 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 <luwei.kang@intel.com>
> > > > ---
> > > >  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.

Yes, CPUID data is not sent as part of migration stream. But when will the "-cpu qemu,+intel-pt" result different results? I think CPU type include some specific features and CPUID data of Intel PT are constant value, so I think the CPUID data should not change as well.

Thanks,
Luwei Kang

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Eduardo Habkost]

On Mon, Jan 28, 2019 at 06:06:56AM +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 <luwei.kang@intel.com>
> > > > > ---
> > > > >  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.
> 
> Yes, CPUID data is not sent as part of migration stream. But
> when will the "-cpu qemu,+intel-pt" result different results? I
> think CPU type include some specific features and CPUID data of
> Intel PT are constant value, so I think the CPUID data should
> not change as well.

Before your patch, "-cpu qemu64,+intel-pt" has CPUID[0].EAX = 0xD,
and guest won't see intel-pt data in CPUID[0x14].

After your patch, "-cpu qemu64,+intel-pt" has CPUID[0].EAX = 0x14,
and guest will see intel-pt data in CPUID[0x14].

-- 
Eduardo

Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Kang, Luwei]

> > > > > > 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 <luwei.kang@intel.com>
> > > > > > ---
> > > > > >  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.
> >
> > Yes, CPUID data is not sent as part of migration stream. But when will
> > the "-cpu qemu,+intel-pt" result different results? I think CPU type
> > include some specific features and CPUID data of Intel PT are constant
> > value, so I think the CPUID data should not change as well.
> 
> Before your patch, "-cpu qemu64,+intel-pt" has CPUID[0].EAX = 0xD, and guest won't see intel-pt data in CPUID[0x14].
> 
> After your patch, "-cpu qemu64,+intel-pt" has CPUID[0].EAX = 0x14, and guest will see intel-pt data in CPUID[0x14].
> 

Oh yes, get it. Thanks.

Luwei Kang

> --
> Eduardo