On Wed, Jun 15, 2016 at 04:25:32PM +0200, Borislav Petkov wrote: [...] > > As to the error message, dear LKP friends, it happens because -cpu kvm64 > on native Intel hands in CPUID bits of the host, i.e., if you do this in > the guest: > > $ grep epb /proc/cpuinfo > flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca > cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm constant_tsc nopl > eagerfpu pni cx16 x2apic hypervisor epb > ^^^ > > you should have "epb" there too which is among those bits.
It shouldn't. -cpu kvm64 should give exactly the same set of CPUID bits on every host (unless you see "missing feature" warnings. "-cpu kvm64,enforce" would be even more strict and refuse to start if any feature is missing). > > I can reproduce the same issue on an AMD host too by booting my guest > with > > "-cpu kvm64,vendor=GenuineIntel" > > Paolo, Eduardo, question: can we hide certain CPUID bits from the guest > when booting with -cpu kvm64? > > In general, is there a way I can set or clear arbitrary CPUID bits so > that the guest sees what I want it to see? > > And I don't mean the predefined CPUID flags which you toggle with "+" or > "-" followed by flag name. Because -cpu kvm64,-epb doesn't work. If -cpu kvm64,-epb doesn't work, -cpu kvm64 is not supposed to expose ebp to the guest in the first place. CPUID[6].ECX, specifically, is hardcoded to 0 in QEMU. > > Is there a way to make this work or should we hack it into qemu so that > we are able to do that? I.e., something like > > -cpu=kvm64,cpuid=leaf6_ecx_bit3=0,... > > or something smarter. But you get the idea... We have that: it is "-feature" (or "feature=off"). Features that can't be configured in the command-line should never appear to the guest unless you use "-cpu host,migratable=off". Something that allows disabling feature flags that still don't have a name in QEMU would be useful for "-cpu host,migratable=off" only (and that's an interesting suggestion). But that's not the case here, I guess. -- Eduardo
