* Huanyu ZHAI ([email protected]) wrote: > Subject: [PATCH] cpu/i386: update xsave components after CPUID filtering > > On i386 platform, CPUID data are setup through three consecutive steps: CPU > model definition, expansion and filtering. > XSAVE components are enabled during the expansion stage, by checking if they > are enabled in CPUID. However, it is still > probable that some XSAVE features will be enabled/disabled during the > filtering stage and the XSAVE components left unchanged. > Inconsistency between XSAVE features and enabled XSAVE components can lead to > problems on some Linux guests in the absence of > the following patch in the kernel: > > https://www.mail-archive.com/[email protected]/msg1452368.html > > A simple case to reproduce this problem is to start a SUSE 12 SP3 guest with > cpu model set to Skylake-Server: > $ qemu-system-x86_64 -cpu Skylake-Server ... > > In the SUSE 12 SP3 guest, one can observe that PKRU will be enabled without > Intel PKU's presence. > That's because on platform with Skylake-Server cpus, Intel PKU is disabled > during x86_cpu_filter_features(), > but the XSAVE PKRU bit was enabled by x86_cpu_expand_features().
I just spotted this when trying to clear out my mail folder; this isn't a 'trivial'! I'm not sure if it's right or not, but I've cc'd in Paolo and Marcelo as x86 maintainers. Dave > Signed-off-by: Huanyu ZHAI [email protected]<mailto:[email protected]> > Signed-off-by: Xin Wang > [email protected]<mailto:[email protected]> > --- > target/i386/cpu.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 22b681ca37..2ee574cf05 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -6362,6 +6362,9 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool > verbose) > mark_unavailable_features(cpu, FEAT_7_0_EBX, > CPUID_7_0_EBX_INTEL_PT, prefix); > } > } > + > + /* Update XSAVE components again based on the filtered CPU feature flags > */ > + x86_cpu_enable_xsave_components(cpu); > } > > static void x86_cpu_hyperv_realize(X86CPU *cpu) > -- > 2.27.0 > -- Dr. David Alan Gilbert / [email protected] / Manchester, UK
