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Re: [libvirt] [PATCH] Add new 'kvm' domain feature and ability to hide KVM signature



On 08/15/2014 12:32 PM, Alex Williamson wrote:
> QEMU 2.1 added support for the kvm=off option to the -cpu command,
> allowing the KVM hypervisor signature to be hidden from the guest.
> This enables disabling of some paravirualization features in the
> guest as well as allowing certain drivers which test for the
> hypervisor to load.  Domain XML syntax is as follows:
> 
> <domain type='kvm>
>   ...
>   <features>
>     ...
>     <kvm>
>       <hidden state='on'/>
>     </kvm>
>   </features>
>   ...
> 
> Signed-off-by: Alex Williamson <alex williamson redhat com>
> ---
> 
> If it's not obvious, this patch is derived from copying and modifying
> the similar hyperv feature support.  Hopefully I've found all the
> right pieces.
> 

Seems to cover all the bases. couple minor bits:

>  docs/formatdomain.html.in                          |   21 ++++
>  docs/schemas/domaincommon.rng                      |   18 +++-
>  src/conf/domain_conf.c                             |  100 ++++++++++++++++++++
>  src/conf/domain_conf.h                             |    9 ++
>  src/qemu/qemu_command.c                            |   22 ++++
>  tests/qemuargv2xmltest.c                           |    2 
>  .../qemuxml2argv-kvm-features-off.args             |    5 +
>  .../qemuxml2argv-kvm-features-off.xml              |   27 +++++
>  .../qemuxml2argv-kvm-features.args                 |    5 +
>  .../qemuxml2argvdata/qemuxml2argv-kvm-features.xml |   27 +++++
>  tests/qemuxml2argvtest.c                           |    3 +
>  tests/qemuxml2xmltest.c                            |    3 +
>  12 files changed, 240 insertions(+), 2 deletions(-)
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-kvm-features-off.args
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-kvm-features-off.xml
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-kvm-features.args
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-kvm-features.xml
> 
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index bd99ae0..32cc381 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -1232,6 +1232,9 @@
>        &lt;vapic state='on'/&gt;
>        &lt;spinlocks state='on' retries='4096'/&gt;
>      &lt;/hyperv&gt;
> +    &lt;kvm&gt;
> +      &lt;hidden state='on'/&gt;
> +    &lt;/kvm&gt;
>      &lt;pvspinlock/&gt;
>  
>    &lt;/features&gt;
> @@ -1310,7 +1313,23 @@
>            can be explicitly disabled by using <code>state='off'</code>
>            attribute.
>        </dd>
> -
> +      <dt><code>kvm</code></dt>
> +      <dd>Various features to change the behavior of the KVM hypervisor.
> +      <table class="top_table">
> +        <tr>
> +          <th>Feature</th>
> +          <th>Description</th>
> +          <th>Value</th>
> +          <th>Since</th>
> +        </tr>
> +        <tr>
> +          <td>hidden</td>
> +          <td>Hide the KVM hypervisor from standard MSR based discovery</td>
> +          <td> on, off</td>
> +          <td><span class="since">2.1.0 (QEMU only)</span></td>
> +        </tr>
> +      </table>
> +      </dd>
>      </dl>
>  

I'd specify that the default value is 'off' if using KVM, 'on' otherwise, and
can be explicitly disabled with 'on'.


> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 8a69976..77a84cc 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -6228,6 +6228,25 @@ qemuBuildCpuArgStr(virQEMUDriverPtr driver,
>          }
>      }
>  
> +    if (def->features[VIR_DOMAIN_FEATURE_KVM] == VIR_TRISTATE_SWITCH_ON) {
> +        if (!have_cpu) {
> +            virBufferAdd(&buf, default_model, -1);
> +            have_cpu = true;
> +        }
> +
> +        for (i = 0; i < VIR_DOMAIN_KVM_LAST; i++) {
> +            switch ((virDomainKVM) i) {
> +            case VIR_DOMAIN_KVM_HIDDEN:
> +                if (def->kvm_features[i] == VIR_TRISTATE_SWITCH_ON)
> +                    virBufferAsprintf(&buf, ",kvm=off");
> +                break;
> +

There's a 'make syntax-check' warning here with latest git:

src/qemu/qemu_command.c:6241:                    virBufferAsprintf(&buf,
",kvm=off");
maint.mk: use virBufferAddLit, not virBufferAsprintf, with a string literal
make: *** [sc_prohibit_virBufferAsprintf_with_string_literal] Error 1

The rest looks fine, I'll commit v2 if no one has objections to the XML or
code (CCing Peter and Jan who did some of the hyperv work)

- Cole


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