On Mon, 27 Mar 2017 11:48:15 -0300
Eduardo Habkost <ehabk...@redhat.com> wrote:
> The existing code for "host" and "max" CPU models overrides every
> single feature in the CPU object at realize time, even the ones
> that were explicitly enabled or disabled by the user using
> "feat=on" or "feat=off", while features set using +feat/-feat are
> kept.
>
> This means "-cpu host,+invtsc" works as expected, while
> "-cpu host,invtsc=on" doesn't.
>
> This was a known bug, already documented in a comment inside
> x86_cpu_expand_features(). What makes this bug worse now is that
> libvirt 3.0.0 and newer now use "feat=on|off" instead of
> +feat/-feat when it detects a QEMU version that supports it (see
> libvirt commit d47db7b16dd5422c7e487c8c8ee5b181a2f9cd66).
>
> Change the feature property getter/setter to set a
> env->user_features field, to keep track of features that were
> explicitly changed using QOM properties. Then make the
> max_features code not override user features when handling "-cpu
> host" and "-cpu max".
>
> This will also allow us to remove the plus_features/minus_features
> hack in the future, but I plan to do that after 2.9.0 is
> released.
>
> Reported-by: Jiri Denemark <jdene...@redhat.com>
> Signed-off-by: Eduardo Habkost <ehabk...@redhat.com>
Reviewed-by: Igor Mammedov <imamm...@redhat.com>
> ---
> Changes v1 -> v2:
> * Don't clear existing bits on env->features (they are already
> supposed to be all zeroes) (Igor)
> * Fix typo on comment (Igor)
> * Moved feature word getter/setter parameter changes to separate
> patch (Igor)
> ---
> target/i386/cpu.h | 2 ++
> target/i386/cpu.c | 13 +++++++++----
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 07401ad9fe..c4602ca80d 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1147,6 +1147,8 @@ typedef struct CPUX86State {
> uint32_t cpuid_vendor3;
> uint32_t cpuid_version;
> FeatureWordArray features;
> + /* Features that were explicitly enabled/disabled */
> + FeatureWordArray user_features;
> uint32_t cpuid_model[12];
>
> /* MTRRs */
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index feefa5b8a4..13c0985f11 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -3373,15 +3373,19 @@ static void x86_cpu_expand_features(X86CPU *cpu,
> Error **errp)
> GList *l;
> Error *local_err = NULL;
>
> - /*TODO: cpu->max_features incorrectly overwrites features
> - * set using "feat=on|off". Once we fix this, we can convert
> + /*TODO: Now cpu->max_features doesn't overwrite features
> + * set using QOM properties, and we can convert
> * plus_features & minus_features to global properties
> * inside x86_cpu_parse_featurestr() too.
> */
> if (cpu->max_features) {
> for (w = 0; w < FEATURE_WORDS; w++) {
> - env->features[w] =
> - x86_cpu_get_supported_feature_word(w, cpu->migratable);
> + /* Override only features that weren't set explicitly
> + * by the user.
> + */
> + env->features[w] |=
> + x86_cpu_get_supported_feature_word(w, cpu->migratable) &
> + ~env->user_features[w];
> }
> }
>
> @@ -3731,6 +3735,7 @@ static void x86_cpu_set_bit_prop(Object *obj, Visitor
> *v, const char *name,
> } else {
> cpu->env.features[fp->w] &= ~fp->mask;
> }
> + cpu->env.user_features[fp->w] |= fp->mask;
> }
>
> static void x86_cpu_release_bit_prop(Object *obj, const char *name,
