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[libvirt] [PATCH] cpu: add CLZERO CPUID support for AMD platforms

Ani Sinha posted 1 patch 4 years, 4 months ago
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git fetch https://github.com/patchew-project/libvirt tags/patchew/1575371352-99055-1-git-send-email-ani.sinha@nutanix.com
src/cpu_map/x86_EPYC-IBPB.xml | 1 +
src/cpu_map/x86_EPYC.xml      | 1 +
src/cpu_map/x86_features.xml  | 3 +++
3 files changed, 5 insertions(+)
[libvirt] [PATCH] cpu: add CLZERO CPUID support for AMD platforms
Posted by Ani Sinha 4 years, 4 months ago 
Qemu commit e900135dcfb67 ("i386: Add CPUID bit for CLZERO and XSAVEERPTR")
adds support for CLZERO CPUID bit.
This commit extends support for this CPUID bit into libvirt.

Signed-off-by: Ani Sinha <ani.sinha@nutanix.com>
---
 src/cpu_map/x86_EPYC-IBPB.xml | 1 +
 src/cpu_map/x86_EPYC.xml      | 1 +
 src/cpu_map/x86_features.xml  | 3 +++
 3 files changed, 5 insertions(+)

diff --git a/src/cpu_map/x86_EPYC-IBPB.xml b/src/cpu_map/x86_EPYC-IBPB.xml
index 283697e..a70fbd8 100644
--- a/src/cpu_map/x86_EPYC-IBPB.xml
+++ b/src/cpu_map/x86_EPYC-IBPB.xml
@@ -14,6 +14,7 @@
     <feature name='bmi2'/>
     <feature name='clflush'/>
     <feature name='clflushopt'/>
+    <feature name='clzero'/>
     <feature name='cmov'/>
     <feature name='cr8legacy'/>
     <feature name='cx16'/>
diff --git a/src/cpu_map/x86_EPYC.xml b/src/cpu_map/x86_EPYC.xml
index f060139..6c11d82 100644
--- a/src/cpu_map/x86_EPYC.xml
+++ b/src/cpu_map/x86_EPYC.xml
@@ -14,6 +14,7 @@
     <feature name='bmi2'/>
     <feature name='clflush'/>
     <feature name='clflushopt'/>
+    <feature name='clzero'/>
     <feature name='cmov'/>
     <feature name='cr8legacy'/>
     <feature name='cx16'/>
diff --git a/src/cpu_map/x86_features.xml b/src/cpu_map/x86_features.xml
index 2bed1e0..dd62755 100644
--- a/src/cpu_map/x86_features.xml
+++ b/src/cpu_map/x86_features.xml
@@ -473,6 +473,9 @@
   <feature name='ibpb'>
     <cpuid eax_in='0x80000008' ebx='0x00001000'/>
   </feature>
+  <feature name='clzero'>
+    <cpuid eax_in='0x80000008' ebx='0x00000001'/>
+  </feature>
   <feature name='amd-ssbd'>
     <cpuid eax_in='0x80000008' ebx='0x01000000'/>
   </feature>
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Re: [libvirt] [PATCH] cpu: add CLZERO CPUID support for AMD platforms
Posted by Jiri Denemark 4 years, 4 months ago 
On Tue, Dec 03, 2019 at 03:09:12 -0800, Ani Sinha wrote:
> Qemu commit e900135dcfb67 ("i386: Add CPUID bit for CLZERO and XSAVEERPTR")
> adds support for CLZERO CPUID bit.
> This commit extends support for this CPUID bit into libvirt.
> 
> Signed-off-by: Ani Sinha <ani.sinha@nutanix.com>
> ---
>  src/cpu_map/x86_EPYC-IBPB.xml | 1 +
>  src/cpu_map/x86_EPYC.xml      | 1 +
>  src/cpu_map/x86_features.xml  | 3 +++
>  3 files changed, 5 insertions(+)
> 
> diff --git a/src/cpu_map/x86_EPYC-IBPB.xml b/src/cpu_map/x86_EPYC-IBPB.xml
> index 283697e..a70fbd8 100644
> --- a/src/cpu_map/x86_EPYC-IBPB.xml
> +++ b/src/cpu_map/x86_EPYC-IBPB.xml
> @@ -14,6 +14,7 @@
>      <feature name='bmi2'/>
>      <feature name='clflush'/>
>      <feature name='clflushopt'/>
> +    <feature name='clzero'/>
>      <feature name='cmov'/>
>      <feature name='cr8legacy'/>
>      <feature name='cx16'/>
> diff --git a/src/cpu_map/x86_EPYC.xml b/src/cpu_map/x86_EPYC.xml
> index f060139..6c11d82 100644
> --- a/src/cpu_map/x86_EPYC.xml
> +++ b/src/cpu_map/x86_EPYC.xml
> @@ -14,6 +14,7 @@
>      <feature name='bmi2'/>
>      <feature name='clflush'/>
>      <feature name='clflushopt'/>
> +    <feature name='clzero'/>
>      <feature name='cmov'/>
>      <feature name='cr8legacy'/>
>      <feature name='cx16'/>

We don't normally change existing CPU models as it can cause issues with
migration between non-matching versions of libvirt. If QEMU enables a
new feature for a given model (which doesn't seem to be the case of
clzero and EPYC, however), you'd automatically get it just by asking for
EPYC in libvirt. Otherwise, you need to ask for clzero explicitly
(adding it to libvirt's EPYC would not cause the feature to be enabled
anyway). Or you can use host-model CPU in which case, clzero will be
automatically added as long as it is supported by QEMU.

> diff --git a/src/cpu_map/x86_features.xml b/src/cpu_map/x86_features.xml
> index 2bed1e0..dd62755 100644
> --- a/src/cpu_map/x86_features.xml
> +++ b/src/cpu_map/x86_features.xml
> @@ -473,6 +473,9 @@
>    <feature name='ibpb'>
>      <cpuid eax_in='0x80000008' ebx='0x00001000'/>
>    </feature>
> +  <feature name='clzero'>
> +    <cpuid eax_in='0x80000008' ebx='0x00000001'/>
> +  </feature>
>    <feature name='amd-ssbd'>
>      <cpuid eax_in='0x80000008' ebx='0x01000000'/>
>    </feature>

We want to keep the bits sorted by their position, I moved it up a bit,
just above wbnoinvd.

Also several cputest results have to be updated since our CPU data
describe some CPUs which already support clzero.

That said, I dropped the changes to EPYC* CPU models, moved the feature
definition in x86_features a bit, updated the test results, and pushed
this as commit 1d17f881a278c408ede19c7e6a5330e3f19fe0f0

Reviewed-by: Jiri Denemark <jdenemar@redhat.com>

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Re: [libvirt] [PATCH] cpu: add CLZERO CPUID support for AMD platforms
Posted by Ani Sinha 4 years, 4 months ago 

> On Dec 16, 2019, at 5:35 PM, Jiri Denemark <jdenemar@redhat.com> wrote:
> 
> On Tue, Dec 03, 2019 at 03:09:12 -0800, Ani Sinha wrote:
>> Qemu commit e900135dcfb67 ("i386: Add CPUID bit for CLZERO and XSAVEERPTR")
>> adds support for CLZERO CPUID bit.
>> This commit extends support for this CPUID bit into libvirt.
>> 
>> Signed-off-by: Ani Sinha <ani.sinha@nutanix.com>
>> ---
>> src/cpu_map/x86_EPYC-IBPB.xml | 1 +
>> src/cpu_map/x86_EPYC.xml      | 1 +
>> src/cpu_map/x86_features.xml  | 3 +++
>> 3 files changed, 5 insertions(+)
>> 
>> diff --git a/src/cpu_map/x86_EPYC-IBPB.xml b/src/cpu_map/x86_EPYC-IBPB.xml
>> index 283697e..a70fbd8 100644
>> --- a/src/cpu_map/x86_EPYC-IBPB.xml
>> +++ b/src/cpu_map/x86_EPYC-IBPB.xml
>> @@ -14,6 +14,7 @@
>>    <feature name='bmi2'/>
>>    <feature name='clflush'/>
>>    <feature name='clflushopt'/>
>> +    <feature name='clzero'/>
>>    <feature name='cmov'/>
>>    <feature name='cr8legacy'/>
>>    <feature name='cx16'/>
>> diff --git a/src/cpu_map/x86_EPYC.xml b/src/cpu_map/x86_EPYC.xml
>> index f060139..6c11d82 100644
>> --- a/src/cpu_map/x86_EPYC.xml
>> +++ b/src/cpu_map/x86_EPYC.xml
>> @@ -14,6 +14,7 @@
>>    <feature name='bmi2'/>
>>    <feature name='clflush'/>
>>    <feature name='clflushopt'/>
>> +    <feature name='clzero'/>
>>    <feature name='cmov'/>
>>    <feature name='cr8legacy'/>
>>    <feature name='cx16'/>
> 
> We don't normally change existing CPU models as it can cause issues with
> migration between non-matching versions of libvirt. If QEMU enables a
> new feature for a given model (which doesn't seem to be the case of
> clzero and EPYC, however), you'd automatically get it just by asking for
> EPYC in libvirt. Otherwise, you need to ask for clzero explicitly
> (adding it to libvirt's EPYC would not cause the feature to be enabled
> anyway). Or you can use host-model CPU in which case, clzero will be
> automatically added as long as it is supported by QEMU.

Right. Thanks for clarifying this.

> 
>> diff --git a/src/cpu_map/x86_features.xml b/src/cpu_map/x86_features.xml
>> index 2bed1e0..dd62755 100644
>> --- a/src/cpu_map/x86_features.xml
>> +++ b/src/cpu_map/x86_features.xml
>> @@ -473,6 +473,9 @@
>>  <feature name='ibpb'>
>>    <cpuid eax_in='0x80000008' ebx='0x00001000'/>
>>  </feature>
>> +  <feature name='clzero'>
>> +    <cpuid eax_in='0x80000008' ebx='0x00000001'/>
>> +  </feature>
>>  <feature name='amd-ssbd'>
>>    <cpuid eax_in='0x80000008' ebx='0x01000000'/>
>>  </feature>
> 
> We want to keep the bits sorted by their position, I moved it up a bit,
> just above wbnoinvd.

Cool. I will keep this in mind next time I send a patch around CPUIDs.

> 
> Also several cputest results have to be updated since our CPU data
> describe some CPUs which already support clzero.
> 
> That said, I dropped the changes to EPYC* CPU models, moved the feature
> definition in x86_features a bit, updated the test results, and pushed
> this as commit 1d17f881a278c408ede19c7e6a5330e3f19fe0f0
> 
> Reviewed-by: Jiri Denemark <jdenemar@redhat.com>

Thanks for pushing this.

Ani



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