Re: [Qemu-devel] [PATCH 1/1] x86: add CPU flags supported inside libvirt

[Eduardo Habkost <ehabkost@redhat.com>, To: "Denis V. Lunev" <den@openvz.org>]

On Thu, Jul 18, 2019 at 04:45:37PM +0300, Denis V. Lunev wrote:
> There are the following flags available in libvirt inside cpu_map.xm
>     <feature name='cvt16'>
>       <cpuid function='0x80000001' ecx='0x00040000'/>

This is bit 18...

>     </feature>
>     <feature name='cmt'> <!-- cqm -->
>       <cpuid eax_in='0x07' ecx_in='0x00' ebx='0x00001000'/>
>     </feature>
> We have faced the problem that QEMU does not start once these flags are
> present in the domain.xml.
> 
> This patch just adds proper names into the map.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Richard Henderson <rth@twiddle.net>
> CC: Eduardo Habkost <ehabkost@redhat.com>
> CC: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
> CC: Peter Krempa <pkrempa@redhat.com>
> CC: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  target/i386/cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 805ce95247..88ba4dad47 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -870,7 +870,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>              "lahf-lm", "cmp-legacy", "svm", "extapic",
>              "cr8legacy", "abm", "sse4a", "misalignsse",
>              "3dnowprefetch", "osvw", "ibs", "xop",
> -            "skinit", "wdt", NULL, "lwp",
> +            "skinit", "wdt", "cvt16", "lwp",

...this is bit 14.

Anyway, the cvt16 bit was removed on purpose, and was never
supported.  See:
http://mid.mail-archive.com/508091FB.1030705@amd.com

>              "fma4", "tce", NULL, "nodeid-msr",
>              NULL, "tbm", "topoext", "perfctr-core",
>              "perfctr-nb", NULL, NULL, NULL,
> @@ -1044,7 +1044,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>              "fsgsbase", "tsc-adjust", NULL, "bmi1",
>              "hle", "avx2", NULL, "smep",
>              "bmi2", "erms", "invpcid", "rtm",
> -            NULL, NULL, "mpx", NULL,
> +            "cmt", NULL, "mpx", NULL,

This is one is named "cqm" on Linux (X86_FEATURE_CQM).  I prefer
to keep consistency with the name already in use by Linux than
the one in libvirt that was never used.

You can still add a "cmt" alias property if you think it would be
useful.

Also, I see no code implementing migration of MSR_IA32_QM_EVTSEL,
MSR_IA32_QM_CTR, or other RDT-M state.  If the feature is not
safe for migration yet, you need to explicitly add the feature to
.unmigratable_flags.


>              "avx512f", "avx512dq", "rdseed", "adx",
>              "smap", "avx512ifma", "pcommit", "clflushopt",
>              "clwb", "intel-pt", "avx512pf", "avx512er",
> -- 
> 2.17.1
> 

-- 
Eduardo