On Fri, 24 Mar 2017 17:36:45 -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>
> ---
> target/i386/cpu.h | 2 ++
> target/i386/cpu.c | 33 +++++++++++++++++++++------------
> 2 files changed, 23 insertions(+), 12 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 7aa762245a..5f2addbf75 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -3373,15 +3373,20 @@ 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 not set explicitly
> + * by the user.
s/not// or if it was intended rephrase to avoid double negation.
> + */
> + env->features[w] &= env->user_features[w];
it probably should be assert to catch features not set via property,
which shouldn't be there in the first place, I don't like silent
filtering that happens here.
> + env->features[w] |=
> + x86_cpu_get_supported_feature_word(w, cpu->migratable) &
> + ~env->user_features[w];
> }
> }
>
> @@ -3692,15 +3697,17 @@ static void x86_cpu_unrealizefn(DeviceState *dev,
> Error **errp)
> }
>
> typedef struct BitProperty {
> - uint32_t *ptr;
> + FeatureWord w;
it would be better if this refactoring and related changes
were in a separate patch, something along lines:
"x86/cpu: use FeatureWord instead of keeping a pointer to cpuid leaf"
> uint32_t mask;
> } BitProperty;
>
> static void x86_cpu_get_bit_prop(Object *obj, Visitor *v, const char *name,
> void *opaque, Error **errp)
> {
> + X86CPU *cpu = X86_CPU(obj);
> BitProperty *fp = opaque;
> - bool value = (*fp->ptr & fp->mask) == fp->mask;
> + uint32_t f = cpu->env.features[fp->w];
> + bool value = (f & fp->mask) == fp->mask;
> visit_type_bool(v, name, &value, errp);
> }
>
> @@ -3708,6 +3715,7 @@ static void x86_cpu_set_bit_prop(Object *obj, Visitor
> *v, const char *name,
> void *opaque, Error **errp)
> {
> DeviceState *dev = DEVICE(obj);
> + X86CPU *cpu = X86_CPU(obj);
> BitProperty *fp = opaque;
> Error *local_err = NULL;
> bool value;
> @@ -3724,10 +3732,11 @@ static void x86_cpu_set_bit_prop(Object *obj, Visitor
> *v, const char *name,
> }
>
> if (value) {
> - *fp->ptr |= fp->mask;
> + cpu->env.features[fp->w] |= fp->mask;
> } else {
> - *fp->ptr &= ~fp->mask;
> + 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,
> @@ -3745,7 +3754,7 @@ static void x86_cpu_release_bit_prop(Object *obj, const
> char *name,
> */
> static void x86_cpu_register_bit_prop(X86CPU *cpu,
> const char *prop_name,
> - uint32_t *field,
> + FeatureWord w,
> int bitnr)
> {
> BitProperty *fp;
> @@ -3755,11 +3764,11 @@ static void x86_cpu_register_bit_prop(X86CPU *cpu,
> op = object_property_find(OBJECT(cpu), prop_name, NULL);
> if (op) {
> fp = op->opaque;
> - assert(fp->ptr == field);
> + assert(fp->w == w);
> fp->mask |= mask;
> } else {
> fp = g_new0(BitProperty, 1);
> - fp->ptr = field;
> + fp->w = w;
> fp->mask = mask;
> object_property_add(OBJECT(cpu), prop_name, "bool",
> x86_cpu_get_bit_prop,
> @@ -3787,7 +3796,7 @@ static void x86_cpu_register_feature_bit_props(X86CPU
> *cpu,
> /* aliases don't use "|" delimiters anymore, they are registered
> * manually using object_property_add_alias() */
> assert(!strchr(name, '|'));
> - x86_cpu_register_bit_prop(cpu, name, &cpu->env.features[w], bitnr);
> + x86_cpu_register_bit_prop(cpu, name, w, bitnr);
> }
>
> static GuestPanicInformation *x86_cpu_get_crash_info(CPUState *cs)
