Is this really needed? QEMU's value of pconfig=on vs. off should be provided by QMP CPU model queries, if a property is not available then Libvirt should not try to set it to off.

Paolo Il gio 26 set 2019, 23:23 Eduardo Habkost <ehabkost(a)redhat.com&gt; ha scritto: > QEMU 3.1.0 was shipped with the "pconfig" CPU property available, > added by commit 5131dc433df5 ("i386: Add CPUID bit for PCONFIG"). > > Then the feature was removed in QEMU 4.0.0 (and 3.1.1), by commit > 712f807e1965 ("Revert 'i386: Add CPUID bit for PCONFIG'"). > > In theory this would be OK, but we do have a problem: existing > software (like libvirt) was already using "pconfig=off" since > QEMU 3.1.0 on some cases. This means software that worked with > QEMU 3.1.0 doesn't work with QEMU 3.1.1 and newer. > > One symptom is the following error being generated by > virt-install while trying to use the 'host-model' CPU model, on a > host that's identified as Icelake-Server: > > ERROR internal error: qemu unexpectedly closed the monitor: \ > 2019-09-24T22:57:42.550032Z qemu-kvm: \ > can't apply global Icelake-Server-x86_64-cpu.pconfig=off: Property > '.pconfig' not found > > Re-add "pconfig" to feature_word_info[FEAT_7_0_EDX].feat_names so > "pconfig=off" will work again. > > This change still won't let users set "monitor=on" because all > accelerators currently report the feature as unsupported. But to > make sure PCONFIG won't be enabled by accident in the future > before we implement the necessary migration code, also add the > feature to .unmigratable_flags. > > Fixes: 712f807e1965 ("Revert 'i386: Add CPUID bit for PCONFIG'") > Signed-off-by: Eduardo Habkost <ehabkost(a)redhat.com&gt; > --- > target/i386/cpu.h | 2 ++ > target/i386/cpu.c | 8 +++++++- > 2 files changed, 9 insertions(+), 1 deletion(-) > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h > index 8e090acd74..b728bd22f1 100644 > --- a/target/i386/cpu.h > +++ b/target/i386/cpu.h > @@ -731,6 +731,8 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS]; > #define CPUID_7_0_EDX_AVX512_4VNNIW (1U << 2) > /* AVX512 Multiply Accumulation Single Precision */ > #define CPUID_7_0_EDX_AVX512_4FMAPS (1U << 3) > +/* PCONFIG Instruction */ > +#define CPUID_7_0_EDX_PCONFIG (1U << 18) > /* Speculation Control */ > #define CPUID_7_0_EDX_SPEC_CTRL (1U << 26) > /* Arch Capabilities */ > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 71034aeb5a..3e25505bd3 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -1084,7 +1084,7 @@ static FeatureWordInfo > feature_word_info[FEATURE_WORDS] = { > NULL, NULL, NULL, NULL, > NULL, NULL, "md-clear", NULL, > NULL, NULL, NULL, NULL, > - NULL, NULL, NULL /* pconfig */, NULL, > + NULL, NULL, "pconfig", NULL, > NULL, NULL, NULL, NULL, > NULL, NULL, "spec-ctrl", "stibp", > NULL, "arch-capabilities", "core-capability", "ssbd", > @@ -1095,6 +1095,12 @@ static FeatureWordInfo > feature_word_info[FEATURE_WORDS] = { > .reg = R_EDX, > }, > .tcg_features = TCG_7_0_EDX_FEATURES, > + /* > + * CPU state altered by the PCONFIG instruction (e.g. MKTME key > table) > + * is not migrated by QEMU yet, so PCONFIG is unmigratable until > + * this is implemented. > + */ > + .unmigratable_flags = CPUID_7_0_EDX_PCONFIG, > }, > [FEAT_7_1_EAX] = { > .type = CPUID_FEATURE_WORD, > -- > 2.21.0 > >